Microdystrophin peptides and methods for treating muscular dystrophy using the same

ABSTRACT

According to the embodiments described herein, a series of biological materials for treatment/therapy of DMD and/or BMD through the recovery of sarcolemmal nNOS is provided. The biological material comprises the complete dystrophin repeats R16 and R17 or certain domains, sections, or fragments of the dystrophin repeats R16 and R17. In some aspects, such domains, sections, or fragments may be selected from sequence motifs including dystrophin R17 α1 helix, α2 and α3 helices of both R16 and R17, or a combination thereof.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Patent Application No. 61/797,012, filed Nov. 26, 2012, which is hereby incorporated by reference in its entirety, as if fully set forth herein.

STATEMENT OF GOVERNMENT INTEREST

The present invention was made with government support under Grant No. ΔR49419 awarded by the National Institutes of Health (NIH). The Government has certain rights in the invention.

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is an X-linked inherited muscle disease caused by mutations of the dystrophin gene. While increased membrane fragility has been considered as a primary pathogenic mechanism of DMD, accumulated evidence suggests that the loss of sarcolemmal nNOS also contributes to the dystrophic process. For example, the mild variant of DMD, Becker Muscular Dystrophy (BMD), results from in-frame mutations of dystrophin, thus expressing the truncated dystrophins in muscle. Many of the truncated dystrophins in BMD lose the ability to tether neuronal nitric oxide synthase (nNOS) to the sarcolemma. Clear evidence shows that deficiency of sarcolemmal nNOS causes muscle ischemia and predominantly contributes to the characteristic symptoms of BMD, such as muscle cramp and pain on exercise, muscle fatigue and reduced exercise endurance. However, current therapies are less effective for muscle ischemia and the resultant symptoms.

Since loss of sarcolemmmal nNOS is responsible for BMD symptoms, recovering sarcolemmal nNOS has been suggested as a plausible approach to treat BMD and DMD. It has been known that sarcolemmal localization of nNOS is sustained by dystrophin, and the inventors' previous studies, through systemic structure-function analysis, have found that dystrophin spectrin-like repeats 16 and 17 (R16/17) are required for sarcolemmal distribution of nNOS. Basically, dystrophins that contain R16/17 show membrane expression of nNOS while those without R16/17 do not. However, the current mini-genes or micro-genes with repeats R16/17 still require the retention of other dystrophin domains. For example, even the smallest nNOS binding dystrophin (ΔR2-R15/ΔR18-R23/ΔC) engineered in previous studies still carries the NT and CR domains, H1, H4, R1 and R24. Furthermore, though the mini-genes or micro-genes previously identified are reduced in size as compared to existing gene therapy, more significant size reduction is desired to increase efficacy of delivery of the therapy.

Therefore, there is a need to provide a series of new biological materials containing certain domains/sections of the dystrophin repeats R16 and R17 for anchoring nNOS to the sarcolemma as a new therapy/treatment for DMD and BMD.

SUMMARY

According to some embodiments, a therapeutic composition is provided herein. In one aspect the therapeutic composition may include an amino acid sequence which comprises dystrophin spectrin-like repeats 16 and 17 (R16/R17) or a functional fragment, component, or domain thereof. In one embodiment, the R16/R17 or a functional fragment, component, or domain thereof is an amino acid sequence motif which comprises RFHYDIKIFN (SEQ ID NO:46). In a further embodiment, the therapeutic composition may further include at least one α helix of dystrophin spectrin-like repeat 16 (R16) and at least one α helix of dystrophin spectrin-like repeat 17 (R17).

In another aspect, the therapeutic composition may include a delivery vehicle. The delivery vehicle may be any suitable moiety that facilitates delivery of the R16/R17 or a functional fragment, component, or domain thereof to a target cell. In some embodiments, the delivery vehicle is a cell-penetrating peptide. In other embodiments, the delivery vehicle is a recombinant adeno-associated viral vector (AAV) that is able to express the R16/R17 or a functional fragment, component, or domain thereof.

According to another embodiment, a method of treating Duchenne Muscular Dystrophy (DMD) Becker Muscular Dystrophy (BMD) is provided. Such a method may include a step of administering a therapeutic amount of a therapeutic composition described above to a subject having DMD or BMD.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) lists the schematic outlines of the microdystrophin constructs of the ΔR2-R15/ΔR18-R23/ΔC and its various deletions; FIG. 1(B) illustrates the microdystrophin genes' representative photomicrographs of GFP, nNOS immunostaining and nNOS activity staining.

FIG. 2(A) lists the schematic outlines of the ΔR2-14/ΔR17-21/ΔC micro-utrophin gene and the chimeric ΔR2-R21/ΔC+Dys R16/17 micro-utrophin gene; FIG. 2(B) are the representative images of flag, utrophin and nNOS immunofluorescence staining and nNOS activity staining.

FIG. 3(A) illustrates the morphological evaluation of nNOS expressions following the infection with R16/17.GFP AAV virus in both ΔH2-R19 transgenic and parental mdx mice; FIG. 3B illustrates the morphological evaluation of nNOS expressions following the infection with R16/17.GFP.Pal AAV virus in both ΔH2-R19 transgenic and parental mdx mice.

FIG. 4(A) lists the amino acid sequence alignment of dystrophin R16/17 and utrophin R15/16, with micro-domains boxed and numbered from I to XIV. FIG. 4(B) includes the representative photomicrographs of dystrophin and nNOS immunostaining, and nNOS activity staining.

FIG. 5 illustrates the yeast-two-hybrid assay measured by β-galactosidase activity by a series of construct with replaced α helices.

FIG. 6(A) includes the representative photomicrographs of dystrophin and nNOS immunostaining and nNOS activity staining in mdx muscle infected by AAV viruses carrying single α helix deletion of R16/17; FIG. 6(B) includes the representative photomicrographs of dystrophin and nNOS immunostaining in mdx muscle infected by AAV viruses carrying single α helix substitution.

FIG. 7 illustrates that that a dystrophin nNOS binding domain does not recruit nNOS to the sarcolemma in microutrophin. Schematic outline of the chimerical microutrophin construct (μ-Utro+Dys R17 microdomain IX). The microdomain IX of utrophin R16 was replaced by the corresponding microdomain of dystrophin R17 in the ΔR2-14/ΔR17-21/ΔC microutrophin gene. Modified microutrophin was delivered to utrophin/dystrophin double null mouse muscle. Shown are the representative Flag, utrophin, and nNOS immunostaining photomicrographs. Asterisks indicate the same myofiber in the serial sections. (Scale bar, 50 μm.)

FIG. 8 shows that substitution of dystrophin R16 or 17 with respective utrophin R15 or R16 compromises nNOS membrane targeting by ΔR2-R15/ΔR18-R23/ΔC microdystrophin. (A) Schematic outline of the μ-Dys+Utro R15 and μ-Dys+Utro R16 chimerical microdystrophin constructs. In the μ-Dys+Utro R15 construct, dystrophin R16 is replaced by utrophin R15. In the μ-Dys+Utro R16 construct, dystrophin R17 is replaced by utrophin R16. (B) Representative images of dystrophin H1, R16, R17, and nNOS immunofluorescence staining and nNOS activity staining on the serial sections of chimerical microdystrophin AAV vector infected mdx muscle. Asterisks indicate the same myofiber in the serial sections. (Scale bar, 50 μm.) (C) Representative Western blot results from whole muscle lysate and microsomal preparation. ΔR4-R23/ΔC and ΔR2-R15/ΔR18-R23/ΔC are two transgenic mouse lines that specifically express microgenes in skeletal muscle. The ΔR4-23/ΔC microdystrophin gene does not contain dystrophin R16/17 (negative control). The ΔR2-R15/ΔR18-R23/ΔC microdystrophin gene contains dystrophin R16/17 (positive control). α-Tubulin was used as the loading control for whole muscle lysate. α1-Na+/K+ ATPase was used as the loading control for microsomal preparation.

FIG. 9 is a table showing a summary of microdystrophin and microutrophin constructs used in the studies described herein.

FIG. 10 is a table showing the impact of indicated mutations on nNOS binding in vivo.

FIG. 11 is a schematic diagram of dystrophin (A) and utrophin (B). Utrophin is a homolog of dystrophin. Dystrophin and utrophin share the similar functional domains. Unlike dystrophin, utrophin is unable to restore sarcolemmal nNOS. Dystrophin R16/17 are involved in sarcolemmal localization of nNOS. In utrophin, R15/16 are highly homological to dystrophin R16/17.

FIG. 12 illustrates that nNOS is predominantly localized at the sarcolemma. Sarcolemmal nNOS is detected by nNOS immunostaining and activity staining. In BL6 mice, nNOS is mainly localized at the sarcolemma while in mdx mice, with the loss of dystrophin, sarcolemmal nNOS is also lost.

FIG. 13 is a table summarizing the expression of dystrophin and sarcolemmal nNOS in different settings.

FIG. 14 is a table illustrating the comparison of two minidystrophin genes, ΔH2-R19 and ΔH2-R15.

FIG. 15A is a schematic showing that sarcolemmal nNOS is absent in ΔH2-R19 transgenic mice. The expression of ΔH2-R19 minidystrophin gene recovers dystroglycan, syntrophin, sarcoglycans and dystobrevin to the sarcolemma. But it cannot restore nNOS to the sarcolemma so nNOS is still in the cytosol FIG. 15B is a schematic showing that sarcolemmal nNOS is restored in ΔH2-R19 transgenic mice by membrane-associated R16/17. Dystrophin R16/R17 are attached with a membrane-targeting motif so R16/17 are associated with the sarcolemma. The expression of membrane-associated R16/17 in ΔH2-R19 transgenic mice restores sarcolemmal nNOS. Therefore, R16/17 recovers the missing nNOS-recruiting function of the ΔH2-R19 minigene. (NT: N-terminus of dystrophin; H: hinge region; CR: cysteine-rich domain; CT: c-terminus of dystrophin).

FIG. 16 shows that dystrophin R16/17 protein is stably expressed in HEK 293 cells. Dystrophin R16, R17, and R16/17 are attached with Flag tag and engineered in pFlag-CMV-2 plasmid. After transfection to HEF 293 cells, cell lysates were detected by anti-Flag antibody. The expressed proteins were detected at the expected size, indicating that dystrophin R16, R17, and R16/17 can be stably expressed in vitro.

FIG. 17 is a schematic showing the configuration of recombinant R16/17 protein. There are two versions of recombinant R16/17 proteins. For TAT.R16/17.GFP.Pal, TAT PTD is connected with N-terminus of R16. GFP tag is attached with C-terminus of R17, and followed by a Pal signal. A His tag will be removed by digestion of proteinase. For TAT.R16/17.Pal, the GFP tag is removed. (His: polyhistidine tag; TAT: TAT protein transduction domain; Pal: palmitoylation signal for membrane targeting.).

FIG. 18 shows a method for determining the optimal dosage and time point to achieve the maximal distribution of R16/17 protein in muscle according to some embodiments. (A) The different dosages will be tested in the studies described herein. (B) The muscle will be harvested according to the above schedule.

FIG. 19 is a table showing the experimental design of the studies described.

FIG. 20 is a schematic showing an AAV construct for expressing R16/17.Pal. The construct carries the muscle specific promoter SPc5-12. Pal signal is located at the 3′ end of the R17 for membrane targeting. The whole expression cassette is flanked by two AAV inverted terminal repeats (ITR). (Pal: Palmitoylation signal for membrane targeting).

FIG. 21 shows the nucleic acid sequence of ΔH2-R19 dystrophin minigene construct (SEQ ID NO:1).

FIG. 22 shows the nucleic acid sequence of ΔH2-R15 dystrophin minigene construct (SEQ ID NO:2).

FIG. 23 shows the nucleic acid sequence of ΔR2-R15/ΔR18-23/ΔC dystrophin microgene construct (SEQ ID NO:3).

FIG. 24 shows the nucleic acid sequence of ΔR4-R23/ΔC dystrophin microgene construct (SEQ ID NO:4).

FIG. 25 shows the nucleic acid sequence of an AV.CMV.ΔR2-15/ΔR18-23/ΔC AAV vector construct (SEQ ID NO:5).

FIG. 26 shows the nucleic acid sequence (SEQ ID NO:6) and the amino acid sequence (SEQ ID NO:7) of human dystrophin spectrin-like repeats 16 and 17 (R16/R17).

FIG. 27 shows the nucleic acid sequence (SEQ ID NO:8) of full-length human dystrophin.

FIG. 28 shows the amino acid sequence (SEQ ID NO:9) of full-length human dystrophin.

FIG. 29 shows the nucleic acid sequences corresponding to the N-terminal (NT), the 24 spectrin like repeats (STRs), the 4 hinge regions, the cysteine-rich (CR), and the C-terminal (SEQ ID NOS:10-40) of human dystrophin.

FIG. 30 shows the amino acid sequences corresponding to each of the functional domains (NT domain, mid rod domain, CR domain and the C-terminal domain) of human dystrophin (SEQ ID NOS:41-44).

FIG. 31 shows the nucleic acid sequence of Δexon 17-48 mini-dystrophin (SEQ ID NO: 45), which is a truncated dystrophin found in BMD.

DETAILED DESCRIPTION

The embodiments described herein provide a series of biological materials that may be used in treatment and/or therapy of DMD and BMD through the recovery of sarcolemmal nNOS. According to some embodiments, the biological materials include a microdystrophin gene, protein, peptide, or functional fragment thereof.

A “dystrophin microgene” or “micro-dystrophin gene” or “microgene” as referred to herein means a nucleic acid molecule that is 5 kb or less in length and encodes a modified or non-full-length dystrophin polypeptide (also referred to as micro-dystrophin protein or polypeptide in the present application). A “micro-dystrophin” as referred to herein means a modified or non-full-length dystrophin protein or peptide molecule that retains biological function of a full-length dystrophin protein and the coding sequence of which is 5 kb or less. A micro-dystrophin may also include a “micro-domain” which refers to a portion or functional fragment of a micro-dystrophin protein or peptide that has biological activity, such as a peptide or protein that includes a relevant binding site (e.g., an nNOS binding site for recruitment of nNOS) or structural units that improve or are required for the biological activity. Examples of microgenes which encode micro-dystrophin proteins that are used in the studies described herein include, but are not limited to, those sequences in FIGS. 23 and 24.

A “dystrophin minigene,” “mini-dystrophin gene,” or “minigene” as referred to herein means a nucleic acid molecule that is more than 5 kb in length but less than the full-length of dystrophin coding sequence, preferably, between 5 kb to about 10 kb in length, more preferably about 5 kb to about 8 kb in length, even more preferably, about 7 kb in length, and encodes a modified or non-full-length dystrophin polypeptide (also referred to as mini-dystrophin protein or peptide in the present application). A “mini-dystrophin” protein or peptide is meant a modified or non-full-length dystrophin protein molecule that retains the biological functions of a full-length dystrophin protein and the coding sequence of which is more than 5 kb in length but less than the full-length of dystrophin coding sequence. Examples of microgenes which encode micro-dystrophin proteins that are used in the studies described herein include, but are not limited to, those sequences in FIGS. 21 and 22.

Dystrophin and its Spectrin-Type Repeats (STRs)

Spectrin-type repeats (STR) are common structural elements found in a variety of proteins, especially cytoskeletal proteins. STRs are composed of 106-122 amino acids folded in a triple α-helical unit. STRs exist either as a single-copy or in tandem repeats. STR-containing proteins play a fundamental role in maintaining the cytoskeletal architecture and organizing protein complexes (Djinovic-Carugo et al. 2002; Le Rumeur et al. 2012). Dystrophin is a vital STR-containing protein in striated muscles that links the cytoskeleton with the extracellular matrix and, hence, preserves sarcolemmal integrity during muscle contraction. Besides mechanical support, dystrophin also scaffolds neuronal nitric oxide synthase (nNOS) and several other signaling proteins to the sarcolemma. The nucleotide and amino acid sequences of human dystrophin are shown in FIGS. 27 and 28, respectively.

Absence of dystrophin results in Duchenne muscular dystrophy (DMD), an X-linked lethal muscle disease (Kunkel 2005). Although increased membrane fragility has been considered as a primary pathogenic mechanism of DMD, accumulated evidence suggests that the loss of sarcolemmal nNOS also contributes to the dystrophic process (Lai et al. 2009; Sander et al 2000; Thomas et al 1998; Li et al. 2011a). A clear understanding of how nNOS is localized to the membrane may thus offer insight to the understanding of the disease and open new therapeutic avenues.

Dystrophin has four functional domains including the N-terminal (NT), middle rod, cysteine-rich (CR), and C-terminal domains (FIG. 30; SEQ ID NOs:41-44). The middle rod domain contains 24 STRs and four interspersed hinges. The nucleic acid sequences of the functional domains and STRs are shown in FIG. 29 (SEQ ID NOs:10-40). It was initially thought that nNOS indirectly binds to the dystrophin C-terminal domain via syntrophin (Hillier et al. 1999; Tochio et al. 1999). However, later studies show that merely restoring syntrophin to the membrane cannot anchor nNOS (Lai et al. 2005; Yue et al. 2006; Judge et al. 2006). Through systemic structure-function analysis, it has been determined that dystrophins that contain STRs 16 and 17 (R16/17) show membrane expression of nNOS but those without R16/17 do not. These findings raise an important question as to why and how R16/17 interacts with nNOS. Therefore, as described in the Examples below, the molecular attributes of dystrophin R16/17 that are responsible for nNOS binding were investigated. In these studies, membrane localized R16/17 was determined the minimal unit for dystrophin-nNOS interaction. It was also found that a 10-residue microdomain in the α1 helix of dystrophin R17 (RFHYDIKIFN; SEQ ID NO:46) contains the nNOS binding site. Further, it was demonstrated that the last two α-helices (α2 and α3 helices) of both R16 and R17 were required to anchor nNOS to the sarcolemma although they are dispensable for nNOS binding in vitro.

Therapeutic Compositions

According to the embodiments described herein, therapeutic compositions for treating DMD and BMD are provided. The therapeutic compositions may include a microdystrophin protein, peptide, microdomain, or a functional fragment thereof that is able to restore nNOS to the sarcolemma. In some embodiments, the microdystrophin protein may be encoded by a corresponding microdystrophin gene. In one embodiment, the microdystrophin protein includes the complete dystrophin repeats R16 and R17 or functional domains, sections, or fragments thereof. In some aspects, functional domains, sections or fragments of dystrophin repeats R16 and R17 that may be used in accordance with the embodiments described herein may include, but are not limited to, the following sequence motifs: a 10-residue microdomain in the α1 helix of dystrophin R17 (RFHYDIKIFN; SEQ ID NO:46), a dystrophin R17 α1 helix, a dystrophin R17 α2 helix, a dystrophin R17 α3 helix, a dystrophin R16 α2 helix, a dystrophin R16 α3 helix, or a combination thereof. In one embodiment, the microdystrophin peptide that is part of the therapeutic composition has an amino acid sequence which comprises dystrophin spectrin-type repeats 16 and 17 (R16/R17) (FIG. 26, SEQ ID NOS:6-7).

According to another embodiment, the microdystrophin peptide that is part of the therapeutic composition includes a dystrophin R17 α1 helix. In such an embodiment, the therapeutic composition may also include a dystrophin R17 α2 helix, a dystrophin R17 α3 helix, a dystrophin R16 α2 helix, a dystrophin R16 α3 helix, or a combination thereof.

According to another embodiment, the microdystrophin peptide that is part of the therapeutic composition includes a sequence motif of RFHYDIKIFN (a ten-residue micro-domain in the dystrophin R17 α1 helix; SEQ ID NO:46). In such an embodiment, the therapeutic composition may also include a dystrophin R17 α2 helix, a dystrophin R17 α3 helix, a dystrophin R16 α2 helix, a dystrophin R16 α3 helix, or a combination thereof.

As described in the Examples below, restoration of sarcolemmal nNOS by dystrophin repeats R16/17 is independent of other domains of dystrophin, such as the dystrophin NT and CR domains, H1, H4, R1 and R24, retained in the mini- or micro-genes in previous studies. To determine whether the regions other than R16/17 contribute to dystrophin-nNOS interaction, in vivo nNOS binding was examined in constructs carrying various deletions based on the smallest nNOS binding dystrophin retaining the NT and CR domains, H1, H4, R1 and R24 (ΔR2-R15/ΔR18-R23/ΔC; SEQ ID NO:3). FIGS. 1(A) and (B). FIG. 1(A) lists the schematic outlines of the microdystrophin constructs of ΔR2-R15/ΔR18-R23/ΔC and its various deletions: deletion of R1/R24, further deletion of NT terminal and H1, or further deletion of CR terminal and H4. FIG. 1(B) illustrates the representative photomicrographs of GFP, nNOS immunostaining and nNOS activity staining from mdx mice infected with the indicated micro-dystrophin AAV virus. As indicated in FIG. 1(B), the removal of R1 and R24 does not compromise sarcolemmal nNOS expression in dystrophin-null mdx muscle; and further deletion of the NT domain and H1 or H4 and the CR domain does not alter nNOS membrane localization either. These results suggest that dystrophin R16/17 can recruit nNOS to the sarcolemma independent of other dystrophin domains.

To further provide that dystrophin R16/17 binds nNOS in a context independent manner, the studies below provide evidence that the dystrophin R16/17 can restore sarcolemmal nNOS in a foreign context. Refer to FIGS. 2(A) and 2(B), which illustrates that dystrophin R16/17 restores sarcolemmal nNOS expression in the context of microutrophin. As shown in FIG. 2(A), a chimeric micro-utrophin gene, in which utrophin R15/16 is replaced by dystrophin R16/17, is engineered with a flag tag at the N-terminal end to facilitate detection. FIG. 2(B) shows that the AAV viruses expressing the parental or the chimeric micro-utrophin genes are delivered to the tibialis anterior muscle of utrophin/dystrophin double knout mice, and the modified micro-utrophin (with R16/17) effectively restored sarcolemmal nNOS expression in utrophin/dystrophin double knockout (u-dko) mouse muscle.

Further, although R16/17 is the only dystrophin component required for sarcolemmal nNOS restoration, attaching a membrane targeting sequence motif assists in localizing nNOS. Refer to FIG. 3A and FIG. 3B, which illustrate the morphological evaluation of nNOS expressions following the infections with R16/17.GFP AAV virus and R16/17.GFP.Pal AAV virus in both ΔH2-R19 transgenic and parental mdx mice. As shown in FIG. 2(A), robust expression of R16/17.GFP is observed in mdx muscle but nNOS is not detected at the sarcolemma; however as indicated in FIG. 2(B), the R16/17 attached with palmitoylation membrane targeting sequence at the C-terminus, R16/17.GFP.Pal, is transduced into mdx muscle, and most importantly sarcolemmal nNOS is detected in both ΔH2-R19 transgenic and parental mdx mice. Thus, attaching membrane targeting sequence motif to R16/17 may further assist the restoration of sarcolemmal nNOS.

The studies described below also identifies the nNOS-binding domain, a ten-residue sequence motif, RFHYDIKIFN (SEQ ID NO:46), located in the dystrophin R17 α1 helix. FIGS. 4(A) and 4(B), illustrates a panel of micro-domain substitution studies revealing the nNOS binding site in dystrophin R17 α1 helix. FIG. 4(A) lists the amino acid sequence alignment of dystrophin R16/17 and utrophin R15/16, with micro-domains boxed and numbered from I to XIV. 14 chimerical micro-dystrophin constructs have been generated, where the individual micro-domain in dystrophin R16/17 has been replaced by the corresponding micro-domain of utrophin R15/16 in the ΔR2-R15/ΔR18-R23/ΔC micro-dystrophin gene. FIG. 4(B) illustrates the representative photomicrographs of dystrophin and nNOS immunostaining, and nNOS activity staining, after the modified microgenes being transferred to the mdx muscle. As shown in FIG. 4(B), the photomicrographic patterns are not altered in 13 out the 14 constructs, while the construct IX, in which the ten-residue micro-domain in the first half of dystrophin R17 α1 helix is replaced, is the only exception. With replacement of the ten-residue, RFHYDIKIFN (SEQ ID NO:46), membrane-associated nNOS expression is completely abolished in muscles treated with this construct. This suggests that the ten-reside (RFHYDIKIFN; SEQ ID NO:46) micro-domain in construct IX contains the nNOS-binging site.

The Examples provide additional evidence that dystrophin R17 α1 helix contains the nNOS-binding site via an in vitro yeast two-hybird assay. As shown in FIG. 5, a series of α helix substitution constructs was generated by replacing one of the α helices of dystrophin R16/17 with the corresponding α helix from dystrophin R18. Interaction with nNOS is not disrupted in most cases except when R17 α1 helix is replaced (FIG. 5).

In addition to dystrophin R17 micro-domain IX in α1 helix, other structural features of dystrophin R16/17, such as the α2 and α3 helices of both R16 and R17, may also be needed for sarcolemmal nNOS localization. FIG. 6(A) illustrates an in vivo binding assay using AAV gene transfer with mini-genes carrying single α helix deletion. As shown in FIG. 6(A), nNOS binding is abolished in all the deletion constructs, which suggests that either every α helix is required, or more likely, single α helix deletion has shifted the normal phasing of the entire STR and hence disrupted three-dimensional structure of the binding motif.

To further determine the importance of each α helix, a series of α helix substitution micro-dystrophin constructs was generated, where one α helix (or multiple α helices) in dystrophin R16/17 is replaced by the corresponding α helix (or helices) from another dystrophin STR to maintain normal α helix phasing. FIG. 6(B) includes a schematic illustration of the constructs and the representative photomicrographs of dystrophin and corresponding nNOS immunostaining. Substitution of R17 α1 helix destroyed nNOS binding (as aforementioned). Replacement of two or four other α helices also abolished nNOS binding. Single helix substitution of the remaining five α helices revealed more striking results. While R16 α1 helix replacement does not affect nNOS binding, swapping α2 or α3 helix of either R16 or R17 eliminates dystrophin-nNOS interaction. Collectively, the in vivo data (of FIGS. 6(A) and 6(B)) suggest that α2 and α3 helices of both R16 and R17, in addition to α1 helix of R17, may also be important for membrane localization of nNOS in muscle.

In summary, the Examples described below provide a series of biological materials for treatment/therapy of DMD and/or BMD through the recovery of sarcolemmal nNOS. The inventive biological material comprises the complete dystrophin repeats R16 and R17, or alternatively, certain domains/sections of the dystrophin repeats R16 and R17. The aforementioned domains/sections of the dystrophin R16/17 may include a ten-residue carrying the sequence motif of RFHYDIKIFN (SEQ ID NO:46), dystrophin R17 α1 helix, α2 and α3 helices of both R16 and R17 (complete or certain domains or functional fragments thereof), or a combination thereof.

The studies below further provide a series of novel treatment/therapeutic methods for DMD and BMD through restoring the sarcolemmal-nNOS-recruiting function of the truncated dystrophins found in DMD and BMD patients. The restoration of sarcolemmal nNOS may be achieved by delivering a biological material comprising the complete dystrophin repeats R16 and R17, or alternatively certain domains/sections of the dystrophin repeats R16 and R17, to a DMD or BMD patient. The delivery may be achieved by the AAV-mediated gene transfer, the direct delivery of recombinant R16/17 protein or sections thereof via a cell-penetrating peptide, or a direct administration of a certain domain/section of recombinant R16/17 protein.

In certain embodiments, the therapeutic compositions described herein may also include a delivery vehicle to facilitate the delivery of the microdystrophin to target muscle cells. In one embodiment, the delivery vehicle is an adeno-associated viral vector (AAV) or a recombinant adeno-associated AAV (rAAV). In such an embodiment, the AAV vector or rAAV vector includes an expression cassette that includes a microdystrophin gene that expresses the microdystrophin protein.

According to one embodiment, the therapeutic composition for restoring nNOS to sarcolemma comprises an adeno-associated viral vector (AAV) packaged with the dystrophin repeats R16 and R17 without the dystrophin NT and CR domains, H1, H4, R1 or R24. According to another embodiment, the therapeutic composition for restoring nNOS to sarcolemma comprises an AAV packaged with a dystrophin microgene that encodes the complete dystrophin repeats R16 and R17 or functional domains, sections, or fragments thereof. In some aspects, functional domains, sections or fragments of dystrophin repeats R16 and R17 that may be used in accordance with the embodiments described herein may include, but are not limited to, the following sequence motifs: a 10-residue microdomain in the α1 helix of dystrophin R17 (RFHYDIKIFN; SEQ ID NO:46), a dystrophin R17 α1 helix, a dystrophin R17 α2 helix, a dystrophin R17 α3 helix, a dystrophin R16 α2 helix, a dystrophin R16 α3 helix, or a combination thereof. Specific examples of functional domains, sections or fragments of dystrophin repeats R16 and R17 are described above.

In other embodiments, the delivery vehicle is a cell-penetrating peptide. Cell-penetrating peptides (CPPs, also known as protein transduction domains, membrane translocating sequences, and Trojan peptides) short peptides (less than or equal to approximately 40 amino acids), which are able to penetrate a cell membrane to gain access to the interior of a cell. Thus, CPPs may be used to facilitate the transfer of proteins to a muscle cell in vivo. Although expression of R16/17 may be efficiently mediated by AAV gene transfer, safety concerns and immune response to the AAV may potentially arise in clinical applications of AAV gene delivery. Thus, a direct delivery of a microdystrophin protein, peptide or fragment above (such as those described above) via a CPP is an alternative to AAV vector delivery which may make the treatment easier to manipulate and may improve safety profile. CPPs that may be used in accordance with the embodiments described herein include, but are not limited to, Penetratin or Antenapedia PTD (RQIKWFQNRRMKWKK; SEQ ID NO:47), TAT (YGRKKRRQRRR; SEQ ID NO:48) or a modified TAT having one or more mutated residues (e.g., YARAAARQARA, bold indicates mutated residues; SEQ ID NO:49), R9-Tat GRRRRRRRRRPPQ; SEQ ID NO:50), R10 (RRRRRRRRRR; SEQ ID NO:51) SynB1 (RGGRLSYSRRRFSTSTGR; SEQ ID NO:52), SynB3 (RRLSYSRRRF; SEQ ID NO:53), PTD-4 (PIRRRKKLRRLK; SEQ ID NO:54), PTD-5 (RRQRRTSKLMKR SEQ ID NO:55), FHV Coat-(35-49) (RRRRNRTRRNRRRVR; SEQ ID NO:56), BMV Gag-(7-25) (KMTRAQRRAAARRNRWTAR; SEQ ID NO:57), HTLV-II Rex-(4-16) (TRRQRTRRARRNR; SEQ ID NO:58), D-Tat (GRKKRRQRRRPPQ; SEQ ID NO:59), Transportan chimera (GWTLNSAGYLLGKINLKALAALAKKIL; SEQ ID NO:60), MAP (KLALKLALKLALALKLA; SEQ ID NO:61), SBP (MGLGLHLLVLAAALQGAWSQPKKKRKV; SEQ ID NO:62), FBP (GALFLGWLGAAGSTMGAWSQPKKKRKV; SEQ ID NO:63), MPG (ac-GALFLG FLGAAGSTMGAWSQPKKKRKV-cya; SEQ ID NO:64), MPG^((ΔNLS)) (ac-GALFLGFLGAAGSTMGAWSQPKSKRKV-cya; SEQ ID NO:65). Pep-1 (ac-KETWWETWWTEWSQPKKKRKV-cya; SEQ ID NO:66), Pep-2 (ac-KETWFETWFTEWSQPKKKRKV-cya; SEQ ID NO:67), or any other suitable CPP.

In one embodiment, the CPP used as a delivery agent is TAT. To facilitate the efficient delivery of recombinant R16/17 protein to the muscle cell, a cell penetrating peptide, such as the TAT protein transduction domain (PTD), may be attached to or conjugated to R16/17 protein via a covalent linkage (e.g., an intra-molecular form of chemical bonding that is characterized by the sharing or one or more pairs of electrons between two components, producing a mutual attraction that holds the resultant molecule together) or a non-covalent linkage (e.g., an interaction—not covalent in nature—that provide force to hold the molecules or parts of molecules together, such as ionic bonds, hydrophobic interactions, hydrogen bonds, van-der-Waals forces, and dipole-dipole bonds). in accordance with methods known in the art. Where the attachment or conjugation involves a covalent linkage, the CPP and the microdystrophin protein, peptide or functional fragment thereof may be directly coupled to each other or may be coupled via a linker molecule. In some embodiments, a covalent linkage may be between nucleotide molecules. In such case, a nucleotide sequence that encodes the CPP may be operably linked to a microdystrophin gene, so that when expressed by a vector (e.g., a plasmid or a viral vector), the CPP-microdystrophin protein is expressed as a single fusion protein.

Cell penetrating peptides have been used in exon skipping to deliver oligonucleotides to the muscle cell (Wu et al. 2008; Ivanova et al. 2008; Jearawiriyapaisarn et al.; Betts et al. 2012; Moulton 2012; Yin et al. 2008; Yin et al. 2010). In addition, the TAT PTD, when attached to recombinant full-length utrophin and micro-utrophin protein, is able to successfully transfer utrophin proteins to the muscle of mdx mice (Sonnemann et al. 2009). Thus. since the expression of R16/17 protein has been successfully induced by AAV transfer, one skilled in the art would understand that because R16/17 protein may be stably expressed in muscle it could be delivered on its own by the TAT PTD in vivo.

According to another embodiment, the therapeutic composition for restoring nNOS to sarcolemma may further include a membrane targeting signal sequence motif attached to the C-terminus of the dystrophin repeats R16/17 or functional domains, sections, or fragments thereof. The membrane targeting sequence may be any suitable targeting or signaling sequence to direct the therapeutic composition to the sarcolemma membrane to increase its efficacy including, but not limited to, a palmitoylation membrane targeting signal (Pal).

Neuronal nitric oxide synthase (nNOS) is mainly localized at the sarcolemma. Its sarcolemmal localization is sustained by dystrophin. However, the truncated dystrophins, expressed in BMD or DMD treated with exon skipping or gene therapy, lose the nNOS-recruiting ability. Hence, absence of sarcolemmal nNOS is a common manifestation in those patients. Since sarcolemmal nNOS is normally present in muscle and is essential for muscle function, recovering sarcolemmal nNOS in those patients would further ameliorate therapeutic outcome.

Loss of sarcolemmal nNOS is responsible for pathogenesis of muscular dystrophy. Neuronal nitric oxide synthase (nNOS) is predominantly confined to the sarcolemma (FIG. 12), and plays an important role in muscle function. Loss of sarcolemmal nNOS is a common manifestation in both Becker muscular dystrophy (BMD) (Chao et al. 1996; Torelli et al. 2004) and Duchenne muscular dystrophy (DMD) (Brenman et al. 1995), and contributes to pathogenesis of BMD and DMD. In DMD, absence of sarcolemmal nNOS accounts for inability to counteract α-adrenergic-mediated vasoconstriction during muscle contraction, thus resulting in muscle ischemia (Thomas et al. 1998; Sander et al. 2000; Thomas et al. 2003). Additionally, loss of sarcolemmal nNOS leads to muscle fatigue (Kobayashi et al. 2008). In BMD, muscle cramp and fatigue on exercise are mostly attributed to deficiency of sarcolemmal nNOS (Kobayashi et al. 2008).

Absence of dystrophin spectrin-like repeats R16 and R17 (R16/17) causes the deficiency of sarcolemmal nNOS in BMD or DMD receiving exon skipping or gene therapy. Both BMD and DMD are caused by gene mutations in dystrophin, which serves as a scaffold to maintain sarcolemmal localization of nNOS (Brenman et al. 1995; Brenman et al. 1996; Lai et al. 2009).

In DMD, accompanied by dystrophin deficiency, sarcolemmal nNOS is also lost (FIG. 12). In BMD, although there exists truncated dystrophins due to inframe deletion in the middle rod domain, sarcolemmal nNOS is commonly lost, so that deficiency of sarcolemmal nNOS serves as an important criterion for BMD diagnosis (Torelli et al. 2004).

Gene deletion comprises 72% of dystrophin mutations (van Deutekom et al. 2007). The most prominent hotspot of dystrophin deletion is located at the region from exon 45 to 52 (White & den Dunnen 2006). Previously, it was found that dystrophin R16/17 participate in sarcolemmal localization of nNOS (Lai et al. 2009). R16/17 spans the region from exon 42 to 46, which overlaps with this deletion hotspot. Therefore, deletion usually causes partial or complete loss of R16/17, and subsequently leads to absence of sarcolemmal nNOS in both DMD and BMD.

Molecular therapies such as exon skipping or gene therapy can successfully recover dystrophin expression in DMD. Such therapies convert a DMD phenotype to a BMD-like phenotype, thereby prolonging the survival of DMD patients (van Deutekom et al. 2007; Yokota et al. 2009; Yin et al. 2009; Nakamura & Takeda 2011; Cirak et al. 2011; Bhagavati 2012; Goemans et al. 2011; Harper et al. 2002; Gregorevic et al. 2004; Gregorevic et al. 2006; Wand et al. 2000). However, truncated dystrophins induced by these therapies are mostly incapable of restoring sarcolemmal nNOS.

Exon skipping reconstitutes the reading frame of dystrophin by skipping one or more exons that surround the deletion region, thus producing a truncated but functional dystrophin protein. Since deletions often occur in the region encompassing R16/17, the truncated dystrophin proteins recovered by exon skipping are deficient in R16/17, and therefore unable to restore sarcolemmal nNOS. Additionally, efficient gene delivery has been achieved by adeno-associated viral vector (AAV). Due to limited capacity of AAV vectors, truncated dystrophins have to be generated for AAV gene transfer.

Overall, the truncated dystrophins, expressed in BMD or DMD receiving exon skipping or gene therapy, usually lose the ability to restore sarcolemmal nNOS (FIG. 13). Restoration of sarcolemmal nNOS further improves muscle function in the transgenic mice expressing truncated dystrophins. Previously, transgenic mice have been generated to express two different truncated dystrophins (Lai et al. 2009). Similar to BMD, these minidystrophins carry deletions in the middle rod domain. Although the truncated dystrophins improve muscle force and ameliorates dystrophic phenotype, only the minigene with the function to restore sarcolemmal nNOS could further enhance therapeutic efficacy (FIG. 14).

The minigene ΔH2-R19 cannot restore sarcolemmal nNOS. Both blood flow and running performance have been remarkably compromised in ΔH2-R19 transgenic mice. Furthermore, without sarcolemmal nNOS, strenuous exercise gave rise to ischemic lesion in the muscle of ΔH2-R19 transgenic mice (Lai et al. 2009). Consistent with this finding, another study has shown that in the absence of sarcolemmal nNOS, long-term treadmill exercise caused the decline of muscle force and restricted lesion of degeneration and regeneration in utrophin transgenic mice (Li et al. 2010) (FIG. 14).

An R16/17-containing minidystrophin, ΔH2-R15, was also engineered. The minigene ΔH2-R15 restores sarcolemmal nNOS. More importantly, ΔH2-R15 significantly improved blood flow in contracting muscle, boosted exercise performance and prevented muscle ischemic injury following vigorous exercise 9. Hence, restoration of sarcolemmal nNOS further improves therapeutic outcome of truncated dystrophins (FIG. 14).

In BMD or DMD treated with exon skipping or gene therapy, the truncated dystrophins are unable to restore sarcolemmal nNOS. Nitric oxide produced by sarcolemmal nNOS can dilate blood vessel and increase blood flow via activating cGMP-mediated pathway (Kobayashi et al. 2008). Loss of sarcolemmal nNOS compromises this signaling pathway. Those patients are vulnerable to muscle ischemia during exercise.

To date, a clinical trial is testing therapeutic effect of Tadalafil on muscle ischemia of BMD patients. Tadalafil is the inhibitor of 5′-phosphodiesterase (PDE-5) and it can increase the level of cGMP and subsequently improve blood flow (http://clinicaltrials.gov/ct2/show/NCT01070511). But, currently, there is no therapy to restore sarcolemmal nNOS in BMD or DMD receiving exon skipping or gene therapy. Since sarcolemmal nNOS is normally present in muscle and recovery of sarcolemmal nNOS further improves therapeutic efficacy of truncated dystrophins, an adjunct therapy to restore sarcolemmal nNOS would provide therapeutic improvement for those patients.

The missing nNOS-recruiting functionality is transcomplemented by membrane-associated R16/17 in ΔH2-R19 transgenic mice. Previously, it was shown that a ΔH2-R19 minigene loses the ability to restore sarcolemmal nNOS (Lai et al. 2009). In the studies described in the Examples above, it was found that the lost nNOS-recruiting ability of ΔH2-R19 minigene can be recovered by membrane-associated R16/17. An AAV was used to induce the expression of membrane-associated R16/17 in ΔH2-R19 transgenic mice, and which successfully restored sarcolemmal nNOS, indicating that the missing nNOS-recruiting functionality of ΔH2-R19 can be transcomplemented by membrane-targeting R16/17 (FIGS. 15A and 15B).

Since ΔH2-R19 is a truncated dystrophin, similar to the dystrophins in BMD (England et al. 1990), these results have significant potential for restoring sarcolemmal nNOS in the patients with truncated dystrophins but without sarcolemmal nNOS.

Thus, there is an underappreciated gap in treating BMD or DMD receiving exon skipping or gene therapy. They are characterized by the presence of truncated dystrophins but the absence of sarcolemmal nNOS. These patients suffer from muscle ischemia and fatigue during exercise. Sarcolemmal nNOS is normally present in muscle and is critical for muscle function. Furthermore, restoration of sarcolemmal nNOS by an R16/17-inclusive minidystrophin gene (ΔH2-R15) improved blood flow in contracting muscle, boosted running performance, and prevented ischemic injury. So it would be therapeutically significant to restore sarcolemmal nNOS in such patients.

In the studies described below, the expression of dystrophin R16/17 was induced by AAV gene transfer and restore sarcolemmal nNOS in ΔH2-R19 mice. Further, recombinant R16/17 protein may be delivered directly to the muscle cells to restore sarcolemmal nNOS in ΔH2-R19 mice. This direct delivery of the recombinant R16/17 protein may be accomplished using a cell-penetrating peptide, the TAT PTD, which is attached to R16/17 to facilitate the delivery of R16/17 protein to the muscle cell of ΔH2-R19 mice.

Further, blood flow, running performance and ischemic injury may be evaluated in ΔH2-R19 transgenic mice receiving direct delivery of recombinant R16/17 protein. Restoration of sarcolemmal nNOS by transcomplementation of R16/17 would improve therapeutic efficacy, resulting in effects such as improving blood flow and running performance, and preventing ischemic injury. The results gained from this study assist in developing a clinically applicable treatment and shed new light on therapeutic outcome of this novel therapy.

Methods of Treatment

Based on the studies below and in accordance with the embodiments described herein, the microdystrophin proteins, peptides, or fragments thereof or therapeutic compositions which include the same (such as those described herein) may be used in methods for treating Duchenne Muscular Dystrophy (DMD) or Becker Muscular Dystrophy (BMD). Although the studies described herein focus on forms of muscular dystrophy, the methods described herein may be used to treat any disease or condition that is associated with a deficiency, absence or malformation of dystrophin including, but not limited to, muscular dystrophies (e.g., DMD and BMD) and X-linked dilated cardiomyopathy (XLDC).

According to some embodiments, the methods described herein include a step of administering a therapeutically effective amount of the microdystrophin protein, peptide, or fragments thereof to a subject having DMD, BMD, or XLDC. The subject may be a human, mouse, rat, dog, cat, pig, or any other mammal in need of treatment. The microdystrophin protein, peptide, or fragments thereof may be administered alone or as part of a therapeutic composition, which may include a delivery vehicle such as a CPP or an AAV vector as described above.

The microdystrophin protein, peptide, or fragments thereof, may be administered by any suitable route of administration, alone or as part of a therapeutic composition. A route of administration may refer to any administration pathway known in the art, including but not limited to aerosol, enteral, nasal, ophthalmic, oral, parenteral, rectal, transdermal (e.g., topical cream or ointment, patch), or vaginal. “Transdermal” administration may be accomplished using a topical cream or ointment or by means of a transdermal patch. “Parenteral” refers to a route of administration that is generally associated with injection, including infraorbital, infusion, intraarterial, intracapsular, intracardiac, intradermal, intramuscular, intraperitoneal, intrapulmonary, intraspinal, intrasternal, intrathecal, intrauterine, intravenous, subarachnoid, subcapsular, subcutaneous, transmucosal, or transtracheal. In some embodiments, the route of the administration accordance with the methods described herein includes local or regional muscle injection to improve local muscle function in patients, systemic delivery (such as intravenous, intra-artery, intraperitoneal) to all muscles in a region or in the whole body in patients, or in vitro infection of myogenic stem cells with an AAV or lentiviral vector followed by local and/or systemic delivery.

The term “effective amount” as used herein refers to an amount of a microdystrophin protein, peptide, or fragment thereof that produces a desired effect. For example, a population of cells may be contacted with an effective amount of a microdystrophin protein, peptide, or fragment thereof to study its effect in vitro (e.g., cell culture) or to produce a desired therapeutic effect ex vivo or in vitro. An effective amount of a microdystrophin protein, peptide, or fragment thereof may be used to produce a therapeutic effect in a subject, such as preventing or treating a target condition, alleviating symptoms associated with the condition, or producing a desired physiological effect. In such a case, the effective amount of an arginine depleting agent is a “therapeutically effective amount,” “therapeutically effective concentration” or “therapeutically effective dose.” The precise effective amount or therapeutically effective amount is an amount of the microdystrophin protein, peptide, or fragment thereof that will yield the most effective results in terms of efficacy of treatment in a given subject or population of cells. This amount will vary depending upon a variety of factors, including but not limited to the characteristics of the microdystrophin protein, peptide, or fragment thereof (including activity, pharmacokinetics, pharmacodynamics, and bioavailability), the physiological condition of the subject (including age, sex, disease type and stage, general physical condition, responsiveness to a given dosage, and type of medication) or cells, the nature of a pharmaceutically acceptable carrier or carriers in the formulation, and the route of administration. Further, an effective or therapeutically effective amount may vary depending on whether the a microdystrophin protein, peptide, or fragment thereof is administered alone or in combination with a compound, drug, therapy or other therapeutic method or modality. One skilled in the clinical and pharmacological arts will be able to determine an effective amount or therapeutically effective amount through routine experimentation, namely by monitoring a cell's or subject's response to administration of a microdystrophin protein, peptide, or fragment thereof and adjusting the dosage accordingly. For additional guidance, see Remington: The Science and Practice of Pharmacy, 21^(st) Edition, Univ. of Sciences in Philadelphia (USIP), Lippincott Williams & Wilkins, Philadelphia, Pa., 2005, which is hereby incorporated by reference as if fully set forth herein.

“Treating” or “treatment” of a condition may refer to preventing the condition, slowing the onset or rate of development of the condition, reducing the risk of developing the condition, preventing or delaying the development of symptoms associated with the condition, reducing or ending symptoms associated with the condition, generating a complete or partial regression of the condition, or some combination thereof. Treatment may also mean a prophylactic or preventative treatment of a condition.

In some embodiments, the method of treatment may be a stand-alone treatment, or may be used as an adjunct treatment which may complement the nNOS-recruiting function of treatment with truncated dystrophins, and may provide therapeutic benefits for both BMD and DMD. Hence, this therapy holds great promise to become an adjunct therapy for patients receiving currently available treatments.

While the invention has been described in connection with specific embodiments thereof, it will be understood that the inventive materials are capable of further modifications. This patent application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features herein before set forth.

The following examples are intended to illustrate various embodiments of the invention. As such, the specific embodiments discussed are not to be construed as limitations on the scope of the invention. It will be apparent to one skilled in the art that various equivalents, changes, and modifications may be made without departing from the scope of invention, and it is understood that such equivalent embodiments are to be included herein. Further, all references cited in the disclosure are hereby incorporated by reference in their entirety, as if fully set forth herein.

EXAMPLES Example 1 α2 and α3 Helices of Dystrophin R16 and R17 Frame a Microdomain in the α1 Helix of Dystrophin R17 for nNOS Binding Materials and Methods

Animals.

Dystrophin-deficient mdx mice were purchased from The Jackson Laboratory. Utrophin heterozygous mdx mice (mdx/utro+/−) were originally provided by Mark Grady (Washington University, St. Louis, Mo.) (Grady et al. 1997). Experimental utrophin/dystrophin double knockout (u-dko) mice were generated by crossing mdx/utro+/− mice, as previously described (Yue et al. 2006). The skeletal muscle specific mini- and microdystrophin transgenic mdx mice were published previously (Lai et al. 2009; Li et al. 2011a). In these transgenic mice, the mini- or microdystrophin genes were expressed under the transcriptional regulation of the human skeletal α-actin promoter. Three transgenic strains were used in the study. The ΔH2-R19 minidystrophin transgenic mdx mice were used to determine in vivo neuronal NOS (nNOS) binding by the stripped-down R16/17 construct (FIG. 3). This minigene carries the C-terminal domain but does not contain dystrophin R16/17. The ΔR4-23/ΔC and the ΔR2-R15/ΔR18-R23/ΔC microgene transgenic mdx mice were used as negative and positive controls, respectively, for nNOS binding in muscle (FIG. 8B). Dystrophin R16/17 is present in the ΔR2-R15/ΔR18-R23/ΔC microgene but not in the ΔR4-23/ΔC microgene. Experimental mice were housed in a specific pathogen-free animal facility.

Microdystrophins and Microutrophins.

A total of 48 different microdystrophin and microutrophin constructs were used for in vivo nNOS binding assay (FIG. 9). A total of five different microdystrophin constructs were evaluated in vitro for their nNOS binding activity by yeast two-hybrid assay. These microgenes were generated using PCR-based cloning method and all were confirmed by DNA sequencing (FIG. 9). Microgene expression was regulated by the CMV promoter and SV40 polyadenylation signal. For microdystrophin cloning, a human ΔR2-R15/ΔR18-R23/ΔC microgene was used as the backbone (Lai et al. 2009). All dystrophin-related modifications were made according to the human dystrophin sequence. The microutrophin genes were cloned using the full-length mouse utrophin cDNA as the template (a gift of James Ervasti, University of Minnesota, Minneapolis, Minn.) (Rybakova et al. 2002). All utrophin-related modifications were made according to the mouse utrophin sequence.

Recombinant Adeno-Associated Virus Vector and In Vivo Gene Transfer.

The microgene expression cassette was cloned between two inverted terminal repeats in a cis AAV packaging plasmid (Shin et al. 2012). All experimental adeno-associated virus (AAV) vectors were pseudotyped using the Y445F AAV-6 tyrosine mutant capsid (a gift of Arun Srivastava, University of Florida, Gainesville, Fla.) (Zhong et al. 2008; Qiao et al. 2010). AAV vectors were purified through two rounds of CsCl gradient ultracentrifugation and the viral titer was determined by quantitative PCR according a published protocol (6). To test in vivo nNOS binding activity, 1×10¹⁰ vector genome (vg) particles of AAV vectors were directly injected into the tibialis anterior (TA) muscle of 2- to 6-mo-old mdx or transgenic mdx mice, or 3-wk-old u-dko mice (Lai et al. 2005).

AAV-Mediated In Vivo nNOS Binding.

All animal experiments were approved by the University of Missouri Institutional Animal Care and Use Committee. Modified microdystrophins/utrophins were packaged in Y445F AAV-6 vector. The 1010 viral particles were injected to the tibialis anterior muscle to young adult mice. Microgene expression and nNOS expression were examined 5 wk later by immunofluorescence staining, in situ nNOS activity assay, and Western blot (whole-muscle lysate and microsomal preparation) (Lai et al. 2009). Details of each assay are provided below.

Immunofluorescence Staining and nNOS Activity Staining.

Freshly collected muscle samples were embedded in Tissue-Tek OCT (Sakura Finetek) and snap-frozen in 2-methylbutane with liquid nitrogen.GFP was visualized under the FITC channel using aNikon E800 fluorescence microscope. Human dystrophin derived microdystrophin was detected with Dys-3, a human dystrophin-specific monoclonal antibody (1:20; Novocastra). This antibody recognizes an epitope in human dystrophin hinge 1. Dystrophin spectrin-like repeats 16 and 17 were detected with Mandys 102 (1:20) and Manex 44A (1:300) monoclonal antibodies, respectively (gifts from Glenn Morris, The Robert Jones and Agnes Hunt Orthopedic Hospital, Oswestry, Shropshire, United Kingdom) (Lai et al. 2009; Morris et al. 2011). Utrophin was revealed with a mouse monoclonal antibody against the utrophin N-terminal domain (1:20; Vector Laboratories). nNOS was detected with a rabbit polyclonal antibody against an epitope near the C-terminal end of nNOS (1:2,000; Santa Cruz). Histochemical evaluation of nNOS activity was performed according to a published protocol (Lai et al. 2009; Li et al. 2011a; Li et al. 2010; Li et al. 2011b). This staining revealed the NADPH diaphorase activity of nNOS. The Flag tag was revealed with the monoclonal anti-FLAG M2 antibody (1:1.00; Sigma). Photomicrographs were taken with a Qimage Retiga 1300 camera using a Nikon E800 fluorescence microscope.

Western Blot.

Whole-muscle lysate and membrane-enriched microsomal preparations were obtained from snap-frozen TA muscles according to previously published protocols (Lai et al. 2009; Li et al. 2011a; Li et al. 2010; Li et al. 2011b; Li et al. 2009). ΔH2-R19 minidystrophin was detected with an antibody against the C-terminal domain of dystrophin (Dys-2, 1:100; Novocastra). Microdystrophins (including ΔR4-R23/ΔC, ΔR2-R15/ΔR18-R23/ΔC, μ-Dys+Utro R15 and μ-Dys+Utro R16) were probed with the Dys-B antibody that reacts with dystrophin R1 (1:100; Novocastra, Leica Microsystems). Mandys 102 (1:20) and Manex 44A (1:500) monoclonal antibodies were used to detect dystrophin R16 and R17, respectively. nNOS was detected with a rabbit polyclonal antibody against the N-terminal end of nNOS (1:4,000; Upstate, Millipore). α-Tubulin (1:3,000; Sigma) was used as the loading control for whole-muscle lysate Western blot. α1-Na+/K+ ATPase (1:400; Upstate, Millipore) was used as the loading control for microsomal preparation Western blot.

In Vitro nNOS Binding Assay with Yeast Two-Hybrid.

The assay was performed as elaborated in SI Methods. The binding construct carried the nNOS PDZ domain. The activation constructs express various α-helix substituted dystrophin R16/17.

Yeast Two-Hybrid.

A Yeast two-hybrid assay was performed with the Matchmaker GAL4 Two-Hybrid System3 (Clontech) as described previously (Lai et al. 2009). The nNOS PDZ domain [a gift of David Bredt (University of California, San Francisco, Calif.) and Samie R. Jaffrey (Cornell University Weill Medical College, New York, N.Y.)] was cloned into the binding construct (Lai et al. 2009; Brenman et al. 1995). The activation constructs contain the α-helix-modified dystrophin R16/17 in which individual helix within R16/17 was replaced by the corresponding helix from dystrophin R18. A total of five different activation constructs were generated. In each construct, one of the following dystrophin helices including R16α1, R16α2, R16α3, R17α1, or R17α2 was replaced. All constructs were sequenced before use. The positive control for the yeast two-hybrid assay was performed using the syntrophin PDZ domain as the activation construct according to a previous publication (Lai et al. 2009). To detect positive interaction, the binding construct and one of the referred activation construct were cotransfected to yeast cells. The qualitative plate assay and the semiquantitative dot assay were performed on the leucine/tryptophan/histidine triple-deficient medium. The quantitative β-galactosidase activity assay was measured using the Galacto-light system (Applied Biosystems).

Results

Membrane Expression of Dystrophin R16/17 Alone is Sufficient to Target nNOS to the Sarcolemma.

Although previous studies suggest that dystrophin R16/17 is necessary for membrane-associated nNOS expression (Lai et al. 2009; Li et al. 2011a), those skilled in the art at that time would have appreciated that other repeats, hinges or domains would have also been required. This is evidenced by the fact that prior to the studies described herein, the smallest nNOS binding dystrophin (ΔR2-R15/ΔR18-R23/ΔC) also carries the NT and CR domains, H1, H4, R1, and R24 (FIG. 1 and FIG. 9) (Lai et al. 2009). To determine whether these regions contributed to dystrophin-nNOS interaction, in vivo nNOS binding in constructs carrying additional deletions was examined. Removing R1 and R24 did not compromise sarcolemmal nNOS expression in dystrophin-null mdx muscle. Further deletion of the NT domain and H1 or H4 and the CR domain did not alter nNOS membrane localization either (FIG. 1). These results suggest that dystrophin R16/17 can recruit nNOS to the sarcolemma independent of other dystrophin domains.

Next, a stripped-down construct of only dystrophin R16/17 was used to determine whether it can localize nNOS to the sarcolemma. To facilitate detection, a GFP tag was fused to dystrophin R16/17 (R16/17.GFP) (FIG. 3A and FIG. 9). Robust expression of R16/17. GFP was observed in mdx muscle but nNOS was not detected at the sarcolemma (FIG. 3A). Loss of dystrophin results in the disassociation of syntrophin from the membrane. Syntrophin is also required for sarcolemmal nNOS localization (Adams et al. 2000; Kameya et al. 1999). To more stringently test the R16/17.GFP construct, it was introduced to skeletal muscle specific ΔH2-R19 minidystrophin transgenic mdx mice (FIG. 3A) (Lai et al. 2009). The ΔH2-R19 minidystrophin gene does not restore nNOS to the membrane but it anchors syntrophin to the sarcolemma (Lai et al. 2009; Lai et al. 2005; Harper et al. 2002). The R16/17.GFP AAV virus successfully transduced transgenic mdx muscle. However, the virus still did not restore nNOS to the sarcolemma (FIG. 3A). R16/17.GFP expression was limited to the sarcoplasm only. Failure to localize nNOS to the sarcolemma may be due to the lack of membrane targeting of R16/17.GFP. To address this possibility, a palmitoylation membrane targeting sequence was attached to the C terminus of R16/17.GFP to generate R16/17.GFP.Pal (FIG. 3B and FIG. 9) (Hancock et al. 1990). Compared with R16/17.GFP, palmitoylated dystrophin R16/17 was clearly enriched at the sarcolemma (FIG. 3B). Membrane-associated nNOS was detected in R16/17.GFP.Pal-treated ΔH2-R19 transgenic mdx mice (FIGS. 3B and 3C). Collectively, this data suggest that R16/17 is the only dystrophin component required for sarcolemmal nNOS targeting (Lai et al. 2009).

Dystrophin R17 α1 Helix Contains the nNOS-Binding Domain. Utrophin is an autosomal paralog of dystrophin. Utrophin R15/16 is homologous to dystrophin R16/17. (FIG. 11). However, utrophin R15/16 cannot bring nNOS to the sarcolemma (Li et al. 2010). To test whether dystrophin R16/17 can restore sarcolemmal nNOS in a foreign context, a chimeric microutrophin gene was engineered in which utrophin R15/16 was replaced by dystrophin R16/17 (FIG. 2 and FIG. 9). Modified microutrophin effectively restored sarcolemmal nNOS expression in utrophin/dystrophin double knockout (u-dko) mouse muscle (FIG. 2). These results reiterate that dystrophin R16/17 bind nNOS in a context-independent manner.

To identify the nNOS-binding domain in dystrophin R16/17, 14 chimerical microdystrophin constructs were generated. In these constructs, a microdomain of dystrophin R16/17 was substituted by the corresponding sequence from utrophin R15/16 (FIG. 4A and FIG. 9). Each construct was named after the matching microdomain (I to XIV). Following AAV gene transfer to mdx muscle, sarcolemmal nNOS expression was examined. The pattern was not altered in 13 constructs (FIG. 4B). The only exception is construct IX, in which a 10-residue microdomain in the first half of dystrophin R17 α1 helix was replaced. Membrane-associated nNOS expression was completely abolished in muscles treated with this construct (FIG. 4B). These results suggest that the 10-residue microdomain in construct IX contains the nNOS-binding site (FIG. 4B).

To further establish dystrophin R17 α1 helix microdomain IX as the nNOS-binding domain, this microdomain was engineered into the microutrophin gene. Specifically, the corresponding sequence in utrophin R16 was replaced with that of dystrophin R17 (FIG. 9). Despite strong expression, dystrophin R17 microdomain IX did not anchor nNOS to the sarcolemma in the context of utrophin (FIG. 7). This suggests that in addition to dystrophin R17 microdomain IX, other yet undefined structural features of dystrophin R16/17 are also needed for sarcolemmal nNOS localization.

Sarcolemmal nNOS Binding Requires Five Correctly Phased α-Helices, including α2 and α3 Helices of Dystrophin R16 and all Three α-Helices of Dystrophin R17. The linker between adjacent STRs has been implicated in protein-protein interaction (Stabach et al. 2009; Ipsaro & Mondraon 2010). Therefore, to determine whether the junction between dystrophin R16 and R17 was involved in nNOS binding, four linker mutants (mutants 1-4) were generated to test their effect on nNOS membrane localization. However, none of the mutants altered nNOS membrane localization (FIGS. 9 and 10). These results suggest that the linker between R16 and R17 is not required for nNOS binding.

To decipher other regions that may contribute to nNOS binding, the whole STR was re-examined. The nNOS-binding domain is located in dystrophin R17 (FIG. 4); hence, replacing this STR will destroy nNOS interaction. For this reason, on the focus was directed toward dystrophin R16. Individual replacement of eight microdomains of dystrophin R16 with the corresponding microdomains of utrophin R15 had minimal impact on nNOS binding (FIG. 4). This finding seemed to suggest that dystrophin R16 and utrophin R15 may be exchangeable. To determine the contribution of dystrophin R16 in its entirety, another chimeric microdystrophin (μ-Dys+Utro R15) was generated in which dystrophin R16 was replaced by utrophin R15 (FIG. 9). However, modified microdystrophin only yielded very faint sarcolemmal nNOS staining (FIG. 8A). On microsomal preparation Western blot, modified microdystrophin did not localize nNOS to the sarcolemma (FIG. 8B). These results suggest that dystrophin R16 may tolerate single microdomain substitution but not whole STR exchange by homological utrophin R15.

The α-helix is the basic structural unit of STR. Each STR contains three α-helices, α1, α2, and α3. To determine contribution of individual α-helix on nNOS binding, a series of α-helix substitution constructs were screened by a yeast two-hybrid system (FIG. 5). In these constructs, one of the α-helices of dystrophin R16/17 was replaced by the corresponding α-helix from dystrophin R18. Interaction with nNOS was not disrupted in most cases, except when R17 α1 helix was replaced (FIG. 5).

Considering the possibility that in vitro assay may fail to predict protein interaction in vivo, the in vivo binding assay using AAV gene transfer was performed. First, the impact of single α-helix deletion was examined. Interestingly, nNOS binding was abolished in all of the deletion constructs that were examined (FIG. 6A and Table S1). This finding suggests that either every α-helix is required, or that a single α-helix deletion shifts the normal phasing of the entire STR thereby disrupting 3D structure of the binding motif. To further determine the importance of each α-helix, α-helix substitution microdystrophin constructs were generated. In these constructs, one α-helix (or multiple α-helices) in dystrophin R16/17 was replaced by the corresponding α-helix (or helices) from another dystrophin STR (FIGS. 6B, 9 and 10). This design allows the modified constructs to maintain normal α-helix phasing. Substitution of R17 α1 helix destroyed nNOS binding (FIG. 10). Replacement of other α-helices also abolished nNOS binding (FIG. 10). Single helix substitution of the remaining five α-helices revealed more striking results. Although R16 α1 helix replacement did not affect nNOS binding, swapping the α2 or α3 helix of either R16 or R17 eliminated dystrophin-nNOS interaction (FIG. 6B and FIG. 10). Collectively, the in vivo data described herein suggest that the α2 and α3 helices of both R16 and R17 are important for membrane localization of nNOS in muscle.

Discussion

In this study, the molecular mechanisms underlying dystrophin R16/17-mediated nNOS sarcolemmal localization were investigated. Because dystrophin STRs have never been successfully crystallized (Legrand et al. 2011), an in vivo biochemical approach was taken to study how dystrophin recruits nNOS to the sarcolemma. Specifically, more than 48 different dystrophin and utrophin constructs were generated to express various sequence changes that might be involved in dystrophin-nNOS interaction. These constructs were packaged in muscle tropic AAV viruses and delivered to limb muscles of mdx, u-dko, and ΔH2-R19 minidystrophin transgenic mdx mice. nNOS expression was examined by immunofluorescence staining, in situ enzymatic activity assay, and microsomal preparation Western blot. Positive nNOS binding was defined as the detection of nNOS on the sarcolemma. It was found that membrane bound dystrophin R16/17 anchored nNOS to the sarcolemma in the presence of syntrophin. It was further shown that the α1 helix of dystrophin R17 carries the nNOS-binding microdomain. Finally, it was demonstrated that the function of the nNOS binding microdomain not only required correct phasing of all α-helices in R16/17 but also depended on the structural environment formed by four surrounding helices.

STR is a highly conserved structural module consisting of a triple helical bundle. Interestingly, some paired STRs have evolved unique properties to mediate specific protein-protein interaction while still maintaining their tertiary conformation. The molecular basis for functional specialization of STR is poorly understood. The crystal structure of a ligand-bound STR has only been resolved in one case (Ipsaro & Mondraon 2010). Ipsaro and colleagues recently deciphered the atomic structure of spectrin R14/15 in complex with its binding partner ankyrin (Ipsaro & Mondraon 2010). A negatively charged patch in the α3 helix of spectrin R14 interacts with a positively charged patch in ankyrin. They also show that the linker region between spectrin R14 and R15, and the loop between the α2 and α3 helices of spectrin R15, are important for binding (Ipsaro & Mondraon 2010). The authors propose that: (i) a large tilting between spectrin R14 and R15 brings the linker region and spectrin R15 α2/α3 loop close to each other to form the docking interface, and (ii) ankyrin binding occurs through patch electrostatic interaction (Ipsaro & Mondraon 2010). The results herein revealed a different interaction mode. Specifically, it was found that nNOS recognition was likely accomplished via a 10-residue microdomain in dystrophin R17 α1 helix (FIG. 4). This microdomain is highly conserved through evolution, suggesting it may represent an essential structural feature (Legrand et al. 2011). Based on the fact that dystrophin R17 α1 helix alone supported nNOS binding in vitro in yeast two-hybrid assay (FIG. 5), the 10-residue motif likely contains the authentic nNOS binding site. In contrast to the negatively charged patch in spectrin R14 α3 helix reported by Ipsaro et al., the nNOS binding microdomain identified herein includes amino acids of various electrostatic properties. This finding suggests that dystrophin R16/17 may bind to nNOS through a mechanism different from what was shown for spectrin-ankyrin interaction. Future elucidation of this binding mechanism with X-ray crystallography and NMR may shed new light on understanding other STR-mediated protein interactions.

Another aspect of dystrophin R16/17-nNOS interaction is the difference between in vitro and in vivo assay results. Yeast two-hybrid revealed dystrophin R17 α1 helix is the only component needed for nNOS binding. The requirement for other α-helices was appreciated only when the binding assay was performed in vivo. Because the α1 helix of dystrophin R17 independently recruited nNOS in vitro, α2 and α3 helices of dystrophin R16 and R17 may not directly participate in the binding. Rather, these helices may function to stabilize R16/17 in a specific configuration to facilitate in vivo nNOS binding. Because such information can only be obtained from studies performed in muscle, these results highlight the importance of in vivo biochemical approach in studying protein interaction.

The rod domain of dystrophin was initially considered as a flexible spacer that separates more important functional domains at the N and C termini. However, recent studies suggest that some STRs in the rod domain actually play a more active role in a plethora of cellular functions via interaction with membrane phospholipids, cytoskeletal proteins, and signaling proteins (Le Rumeur et al. 2010). Of particular interest is the ability of dystrophin R16/17 to compartmentalize nNOS to the sarcolemma (Lai et al. 2009). Failure to do so causes functional ischemia and muscle fatigue, hence more severe muscle disease (Lai et al. 2009; Kobayashi et al. 2008). Although previous studies explained why nNOS is delocalized from the membrane in patients carrying deletion mutations involving dystrophin R16/17, they cannot justify cases in which R16/17 is intact yet nNOS is lost from the sarcolemma (Chao et al. 1996; Wells et al. 2003; Torelli et al. 2004). The results from the single α-helix deletion/substitution experiments described herein suggest that an in-frame deletion in other regions of dystrophin may disrupt nNOS interaction by altering α-helix phasing.

The studies discussed herein also reveal several new therapeutic opportunities to treat DMD. Utrophin overexpression has been considered as a promising therapy for DMD. Unfortunately, utrophin cannot bind nNOS (Li et al. 2010). The unique dystrophin R16/17-containing microutrophin gene described herein may thus improve utrophin-based gene therapy. Another possibility is to use membrane-targeted R16/17 as a supplementary (or adjunct) therapy to restore sarcolemmal nNOS expression in situations in which nNOS binding activity is lost in muscle because of deletions affecting dystrophin R16/17 coding region (such as in some Becker muscular dystrophy patients or in DMD patients treated with exon 42-45 skipping).

Example 2 Restoration of Sarcolemmal nNOS by an R16/17-Containing Minidystrophin Improves Blood Perfusion in Contracting Muscle and Boosts Exercise Performance

A minidystrophin gene ΔH2-R19 (FIG. 21) may be generated by a small adaption to the truncated dystrophin gene Δexon17-48 (FIG. 31) found in BMD patients (Harper et al. 2002; England et al. 1990). Because it does not carry R16/17, the ΔH2-R19 minigene is unable to restore sarcolemmal nNOS. In addition, a minidystrophin gene ΔH2-R15 (FIG. 22) was engineered. The ΔH2-R15 minigene contains R16/17 and restores sarcolemmal nNOS. Both minigenes can recover muscle force to the wild-type level and demonstrate almost identical response to eccentric contraction. But in terms of blood perfusion and running performance following strenuous exercise, ΔH2-R15 minigene displays better therapeutic efficacy, indicating that restoration of sarcolemmal nNOS would exert significant therapeutic effect (FIG. 14) (Lai et al. 2009).

Example 3 R16/17 Protein Alone Restores Sarcolemmal nNOS

Restoration of Sarcolemmal nNOS by Dystrophin R16/17 is Independent of Other Domains of Dystrophin.

Sarcolemmal localization of nNOS was achieved by a microdystrophin gene (ΔR2-R15/ΔR18-R23/ΔC; FIG. 23). In addition to R16/17, this microgene also contains other domains, including N-terminus, hinge 1 and 4, R1 and 24, and cysteine-rich domain (FIG. 1A). Although it is known that R16/17 are involved in sarcolemmal nNOS, it remains elusive whether other domains also participate in sarcolemmal localization of nNOS. Sequential deletion of those domains from this microgene was carried out and it was determined whether sarcolemmal nNOS is affected. It was found that other domains of dystrophin are not involved in sarcolemmal nNOS. Consequently, dystrophin R16/17 independently recruit sarcolemmal nNOS (FIG. 1).

Trans-Complementation of Membrane-Bound Dystrophin R16/17 Alone Restores Sarcolemmal nNOS in ΔH2-R19 Transgenic Mice.

Since R16/17-mediated sarcolemmal nNOS is independent of other domains of dystrophin, it was determined whether dystrophin R16/17 alone can restore sarcolemmal nNOS. First an AAV vector carrying R16/17 alone was made, followed by the GFP tag. The AAV viral vectors were delivered to the TA muscles of mdx mice and ΔH2-R19 mini-dystrophin transgenic mice. Both animal models are deficient in sarcolemmal nNOS. Although R16/17.GFP was successfully expressed in the cytosol of myofibers, R16/17 alone cannot restore sarcolemmal nNOS in both animal models (FIG. 3A). Next a membrane-targeting motif, which is the small motif for palmitoylation (Pal), was attached to the 3′-end of R16/17.GFP to deliver the AAV vectors to the TA muscles of mdx and ΔH2-R19 transgenic mice. The palmitoylation motif successfully localized R16/17.GFP to the membrane of myofibers. In mdx mice, membrane bound R16/17 cannot efficiently restore sarcolemmal nNOS. However, in ΔH2-R19 mice, membrane associated R16/17 successfully restored sarcolemmal nNOS, indicating that membrane-bound R16/17 can trans-complement the missing nNOS-recruiting ability of ΔH2-R19 mindystrophin (FIG. 3B).

Example 4 Direct Infusion of Recombinant R16/17 Protein Restores Sarcolemmal nNOS

The study described below, may be performed to determine whether direct delivery of recombinant R16/17 protein can restore sarcolemmal nNOS in ΔH2-R19 transgenic mice when the TAT protein transduction domain (PTD), a cell penetrating peptide, is attached to R16/17.

TAT Protein Transduction Domain (PTD).

In the studies described above, an AAV gene transfer was used to target R16/17 to the muscle membrane. There, membrane associated R16/17 restored sarcolemmal nNOS in ΔH2-R19 transgenic mice. To improve the safety profile and prevent immune response, recombinant R16/17 protein may be delivered directly to muscle to achieve the restoration of sarcolemmal nNOS. To facilitate the transfer of recombinant R16/17 protein to the muscle, the TAT PTD, a cell-penetrating peptide, may be attached to R16/17. The PTD of TAT protein contains a minimum of 11 residues, and is capable of delivering biologically active proteins in vivo (Ho et al. 2001; Morris et al. 2001; Schwarze et al. 1999; Wang et al. 2009). Further, incorporation of the TAT PTD in exon skipping has been shown to increase dystrophin expression in both skeletal and cardiac muscle of mdx mice (Moulton 2012; Sirsi et al. 2008). In addition to transferring oligonucleotides, the TAT PTD has been successfully exploited in delivering the recombinant full-length utrophin and micro-utrophin proteins to the muscle of mdx mice (Sonnemann et al. 2009). Since the molecular size of recombinant R16/17 protein is far less than full-length utrophin and micro-utrophin protein, the cargo capacity of the TAT PTD should be sufficient to transfer recombinant R16/17 protein to the muscle in vivo.

Example 5 Successful Expression of Dystrophin R16/17 Protein in HEK 293 Cells

Dystrophin R16, R17 and R16/17 genes were each cloned into a plasmid pFlag-CMV-2 (Sigma-Aldrich), respectively. In the expression cassette, the Flag tag was fused to the N-terminus of the expressed protein. These three plasmids were transfected into HEK 293 cells and protein expression was detected with anti-Flag antibody. As shown in FIG. 16, the dystrophin R16, R17 and R16/17 proteins were successfully detected, indicating that dystrophin R16/17 can be stably expressed in HEK 293 cells.

R16/17 Protein by Itself is Stable and Eligible to be Delivered by TAT PTD.

It has been reported that individual dystrophin repeats are difficult to express in vitro (Le Rumeur et al. 2010). However, as described above, R16/17 with GFP tag was successfully expressed in muscle by AAV gene transfer (FIG. 3), and R16/17 with Flag tag in HEK 293 cells (FIG. 16), indicating that R16/17 protein is stably present in both in vivo and in vitro systems. Hence, recombinant R16/17 protein may be expressed in in vitro expression systems and then transferred to muscle cells by virtue of an associated TAT PTD in vivo, as described in the Examples below.

Methods

Construction of the Expression Cassette of Recombinant R16/17 Protein.

The 11-residue TAT PTD is connected to N-terminus of R16. GFP tag is attached to C-terminus of R17 to help the trace of R16/17 expression in vivo. And GFP is followed by the membrane-targeting motif, the 17-residue palmitoylation signal (Pal). For the clinical application, the GFP tag should be removed so the recombinant R16/17 protein is made without GFP tag (TAT.R16/17.Pal) (FIG. 17). The coding sequence for TAT.R16/17.GFP.Pal and TAT.R16/17.Pal is placed in the baculoviral donor plasmid (pFastBac), and driven by Polyhedrin (polh) promoter. His tag has been engineered at the N-terminus of expression cassettes and may be used for purification. Since a cutting site of proteinase exists between His tag and TAT PTD, it is very convenient to remove His tag after purification of recombinant protein.

Expression of Recombinant R16/17 Protein.

A baculovirus/insect cell protein expression system (Bac-to-Bac system from Invitrogen) may be used to generate recombinant TAT.R16/17.GFP.Pal and TAT.R16/17.Pal protein. The donor plasmid with the expression cassette may be transformed to E. coli strain DH10Bac containing bacmid and helper to generate recombinant bacmid through site-specific transposition. Then the recombinant bacmid DNA carrying expression cassettes may be extracted from bacteria cells and used for producing recombinant baculoviruses in insect cells. Recombinant bacmid DNA may then be transfected into insect cells, and the recombinant baculoviruses are then collected to determine viral titer via plaque assay. The recombinant baculoviruses may be used to infect insect cells to express recombinant R16/17 protein. After confirming recombinant protein expression by western blot, the production of recombinant baculoviruses may be scaled up through increasing culture volume and repeated rounds of infection. The baculoviruses with high titer are be used to produce a large amount of protein.

Purification of Recombinant TAT.R16/17.GFP.Pal and TAT.R16/17.Pal Protein.

At the time of maximal expression of recombinant protein, insect cells may be harvested for protein purification. The cells may be pelleted by centrifugation. A ProBond purification system may be used to purify recombinant R16/17 protein. Briefly, pelleted cells are lysed by freeze-thaw cycles in provided buffer. Then cell lysates are passed through purification column. Since the recombinant protein is attached with His tag, the recombinant protein is sequestered on the column. Then the recombinant proteins may be eluted from the column by different concentration of imidazole. An SDS-PAGE gel may then be run to analyze the collections of eluted fractions. The identity of the protein may be confirmed by western blot, and then protein fractions are de-salted and resuspended in PBS buffer for further study.

Determination of Transduction Kinetics and Optimal Dosage of Recombinant R16/17 Protein In Vivo.

The optimal injection scheme may be determined as previously described (Sonnemann et al. 2009). The resuspended proteins may be filtered and intraperitoneally injected into 2 week-old ΔH2-R19 mice. The mice receive a single injection of recombinant R16/17 protein at different dosage, ranging from 5-200 μg/g body weight (n=12 for each dosage). The whole body muscle is harvested at 3 hrs, 12 hrs, 24 hrs, 48 hrs, 72 hrs and 96 hrs post injection. The skeletal muscle group, including muscles in the upper arm, forearm, thigh, lower leg, diaphragm, abdominal wall and tongue, and the heart are sectioned and examined by immunostaining with anti-R17 antibody. Positive myofibers may be counted and used for calculating percentage of positive myofibers. By comparing the percentage of positive myofibers, the specific time point and dosage that lead to the highest expression of recombinant R16/17 protein may be decided (See FIG. 18).

Intraperitoneal Infusion of Recombinant R16/17 Protein into ΔH2-R19 Mice.

The optimal dosage of TAT.R16/17.GFP.Pal or TAT.R16/17.Pal protein may be injected intraperitoneally to the ΔH2-R19 mice and the injections may be repeated at one or more optimal time points over the course of three weeks.

Examination of Membrane-Bound R16/17 and Sarcolemmal nNOS in Muscle.

Three days after the last injection, the whole body muscle is harvested as described above. The membrane-bound R16/17.GFP may be detected by fluorescent microscopy for GFP signal, immunostaining and western blot with R17-specific antibody. The membrane-associated R16/17 may be inspected by immunostaining and western blot with R17-specific antibody. Sarcolemmal nNOS may be examined by immunostaining, nNOS activity staining and western blot as previously described (Lai et al. 2009).

Investigation of Possible Toxicity Reaction Caused by Infusion of Recombinant R16/17 Protein.

The toxicity reaction may be carefully weighed by examining behavior change and blood biochemistry profile. The injected mice are kept separately. The behavior and movement may be monitored daily over three weeks. Blood cell count, liver and kidney functions are inspected weekly during three weeks.

Results

As described above, TAT PTD is able to efficiently deliver various proteins to the muscle (Sonnemann et al. 2009; Ho et al. 2001; Morris et al. 2001; Schwarze et al. 1999; Wang et al. 2009). Those proteins have larger molecular weight than recombinant R16/17 protein, indicating that cargo ability of TAT PTD is sufficient to transfer R16/17 protein. Thus, TAT PTD may be used to effectively transfer recombinant R16/17 protein to the muscle cells. Since a membrane-targeting motif is attached to recombinant R16/17 protein, recombinant R16/17 protein may be localized to the sarcolemma. Based on the results of the studies described above, R16/17 protein is stably present in both in vitro and in vivo expression systems. Hence, membrane-bound recombinant R16/17 protein may be used to restore sarcolemmal nNOS in ΔH2-R19 mice.

The membrane-targeting motif that may be used in this study is the palmitoylation motif from K-ras. Membrane targeting of the palmitoylation motif requires a posttranslational modification that adds a farnesyl isoprenoid lipid to the motif (Karnoub & Weinberg 2008; Choy et al. 1999). This prenylation reaction precedes the association of protein with the cell membrane. Because of a lack of palmitoyl transferase machinery in E. coli expression system, the recombinant protein expressed in bacteria is in its non-palmitoylated state (Nishida & Ortiz de Montellano 1998; Navarro-Lerida et al. 2006). Baculovirus/insect cell expression system is a eukaryotic protein expression system and has full posttranslational machinery that can palmitoylate R16/17 protein. Hence, in this study a baculovirus/insect cell expression system may be selected to produce recombinant R16/17 protein.

The yield of recombinant protein may be influenced by multiple factors, such as insect cell lines, virus titer, infection ratio and harvesting time, etc. Thus. this study may be optimized by setting up a series of small-scale experiments to determine optimal cell lines, infection ratio and the best harvesting time to obtain the maximal expression. Further, it is hard to predict the solubility of recombinant R16/17 protein with palmitoylation signal. In a ProBond purification system, the buffer used for purification is decided by solubility of recombinant protein. Therefore, different buffers may be used to determine which buffer can produce high yield of recombinant R16/17 protein.

Example 6 Direct Infusion of Recombinant R16/17 Protein Results in Functional Improvement of Muscle Function

The study described below may be performed to evaluate the functional improvement when sarcolemmal nNOS is recovered by trans-complementation of R16/17 in ΔH2-R19 transgenic mice. Restoration of sarcolemmal nNOS by R16/17 in ΔH2-R19 mice should improve blood flow, improve running performance, and prevent ischemic injury on exercise.

Study Design.

In this study, the therapeutic outcome of recovering sarcolemmal nNOS by R16/17 protein in ΔH2-R19 mice. First, sarcolemmal nNOS may be restored by direct administration of recombinant R16/17 protein in ΔH2-R19 mice. Second, functional studies may be carried out. The therapeutic outcome is then compared between ΔH2-R19 mice treated with recombinant R16/17 protein, and ΔH2-R19 mice with saline injection, ΔH2-R19 mice injected with AAV.R16/17.Pal and ΔH2-R15 mice (FIG. 19). ΔH2-R19 mice cannot restore sarcolemmal nNOS so ΔH2-R19 mice with saline injection serve as a negative control. ΔH2-R15 mice restore nNOS to the sarcolemma and may be used as a positive control.

In the studies described above, an AAV gene transfer was expoited to induce sarcolemmal expression of R16/17 and subsequently restore sarcolemmal nNOS in ΔH2-R19 mice. To comprehensively compare therapeutic efficacy, systemic delivery of AAV.SPc5-12.R16/17.Pal serves as a therapeutic control. Since AAV serotype 9-mediated systemic delivery may result in robust expression of transgene in both skeletal and cardiac muscle (Inagaki et al. 2006; Bostick et al. 2007), an AAV9 may be used as a capsid in the systemic delivery of R16/17. The expression of R16/17 may be driven by muscle-specific promoter SPc5-12 (Foster et al. 2008; Li et al. 1999) to prevent untoward expression of R16/17 in the systemic delivery (FIG. 19).

Functional studies to evaluate the effect of sarcolemmal nNOS on muscle function. The goal of this study is to determine the functional improvement caused by restoration of sarcolemmal nNOS in ΔH2-R19 mice. Sarcolemmal nNOS closely relates to the blood flow of muscle. Deficiency of sarcolemmal nNOS causes ischemic injury upon exercise. Thus, evaluation of blood flow and ischemic injury are the focus of the studies described below, and may include a microsphere experiment, treadmill exercise and histological studies. A microsphere experiment is designed to infuse stable isotope labeled microspheres into the blood stream. The capacity of blood flow in active muscle is reflected by distribution of microspheres, which is determined by measuring the intensity of stable isotope (Lai et al. 2009; Li et al. 1999).

Nitric oxide (NO) produced by sarcolemmal nNOS is antagonistic to the α-adrenergic-mediated vasoconstriction during exercise. Without sarcolemmal nNOS, uncontrolled vasoconstriction may cause muscle ischemia, subsequently affecting muscle performance. Previously, it was found that in the absence of sarcolemmal nNOS, strenuous exercise could lead to ischemic injury, which compromises muscle force and running performance (Lai et al. 2009; Li et al. 2010). Hence, in this study, muscle force and running performance may be examined following long term treadmill exercise. Also the evidence of ischemic injury may be sought by histological studies and real-time PCR. These interrelated studies should comprehensively determine the functional improvement caused by restoration of sarcolemmal nNOS.

Methods

Delivery of R16/17.Pal to the Muscle of ΔH2-R19 Mice.

To examine therapeutic effect of recombinant R16/17 protein, the R16/17 protein is first injected into ΔH2-R19 mice to recover sarcolemmal nNOS. The delivery scheme may be the same as described above. Three days after the last injection, the distribution of R16/17.Pal and sarcolemmal nNOS is inspected. As described above, an AAV-mediated gene transfer is used as a therapeutic control. For AAV gene transfer, a muscle-specific promoter (SPc5-12) may be used to drive muscle-specific expression of R16/17.Pal (FIG. 20) and perform systemic delivery of AAV9 viruses to target R16/17.Pal to the whole body muscle. One month following virus injection, the expression of R16/17.Pal and sarcolemmal nNOS is examined as described above. When restoration of sarcolemmal nNOS is confirmed, the remaining injected mice will undergo the following studies.

Determination of Muscle Force Generation and the Response to Eccentric Contraction.

The muscle force and the response to eccentric contraction may be examined on EDL muscle as previously described (Lai et al. 2009). These studies investigate whether the contractility of muscle is affected by restoration of sarcolemmal nNOS.

Measurement of Blood Perfusion in Contracting Muscle.

To evaluate whether restoration of sarcolemmal nNOS improves blood flow in contracting muscle, blood perfusion of contracting muscle is measured by infusing stable isotope labeled microspheres according to an established protocol (Lai et al. 2009; Roseguini et al. 2010). Briefly, mice are given uphill treadmill training (15 degree grade, 10-15 m/min) daily for continuous 4 days. The running time and intensity is recorded. By training, mice become familiar with treadmill exercise. On the experimental day, a carotid artery catheter is inserted and placed in the ascending aorta. Rhenium-labeled microspheres are infused into the anesthetized mice via the catheter at a constant rate. When the mice are recovered from anesthesia (approximately 3 hrs later), the mice will run treadmill for one minute. The same amount of microspheres labeled with Holmium may be infused during running. Then all the tissues may be harvested for detecting the total and specific tissue intensity of stable isotopes. Tissue perfusion at resting and exercise may be calculated according to previously reported methods (Lai et al. 2009; Roseguini et al. 2010). The absolute muscle perfusion and the capacity to increase blood flow (compared with resting flow) may be compared between experimental and control mice.

Running Performance of Treadmill Exercise.

The injected mice will run uphill treadmill exercise until exhaustion daily for consecutive 10 days. The running distance is documented daily. In presence of sarcolemmal nNOS, running distance is elevated gradually until the end of study. At the end of 10-day treadmill exercise, the muscle samples may be harvested for histological studies and real-time PCR.

Measurement of Muscle Force Following Treadmill.

When sarcolemmal nNOS is restored in ΔH2-R19 mice, those mice are divided into two groups. One group will run horizontal treadmill twice a week for 8 weeks. The other group may be the control without exercise. At the end of 8-week treadmill exercise, muscle force of EDL muscle is compared between these two groups. This study examines whether the presence of sarcolemmal nNOS prevents ischemic injury and maintains muscle force following long-term exercise. The muscle samples may be used further for histological studies and real-time PCR.

Evaluation of ischemic injury by histological studies and real-time PCR. The muscle samples following treadmill exercise and muscle force measurement may be inspected by hematoxylin and eosin (H&E) staining, immunostaining and TUNEL assay. The samples may be examined for macrophage, central nucleation, inflammation infiltration and apoptosis. The total RNA may be extracted and used for real-time PCR analysis of three microRNAs level (miR-21, miR-200c and miR-205), which are the markers for focal ischemic injury in muscle (Hsieh et al. 2010).

Results

The results from this study answer an important question about the therapeutic outcome of this novel therapy. Since this therapy is safe and easy to be administered, it has huge potential to be translated into clinical application.

As described above, a ΔH2-R15 minigene restores sarcolemmal nNOS, and in ΔH2-R15 transgenic mice, sarcolemmal nNOS is evenly distributed (Lai et al. 2009). For therapy based on direct delivery of recombinant R16/17 protein, distribution of sarcolemmal nNOS may be mosaic. In other words, direct administration of recombinant R16/17 protein or functional fragments thereof may restore sarcolemmal nNOS in most of muscle cells although it may be difficult to reach 100% of affected muscle cells. However, this should not be a barrier to successful treatment, as it has been found that only 30% dystrophin level can prevent muscular dystrophy in human patients (Neri et al. 2007). So it is possible that a therapeutic effect is exerted when sarcolemmal nNOS reaches the same level. Additionally, ΔH2-R19 mice with saline injection are included as a negative control, ΔH2-R19 mice with AAV.R16/17.Pal gene delivery are included as a therapeutic control and ΔH2-R15 mice are included as a positive control. By comparing with control groups, one skilled in the art would be able to determine a dose and administration that responsible for therapeutic efficacy.

SUMMARY

There is a gap in treating BMD patients or DMD receiving exon skipping or gene therapy since those patients are characterized by the presence of truncated dystrophins but the absence of sarcolemmal nNOS. Results of the studies described herein fill this gap and may be extrapolated to develop therapies in large animal model and human patients.

REFERENCES

The references, patents and published patent applications listed below, and all references cited in the specification above are hereby incorporated by reference in their entirety, as if fully set forth herein.

-   Adams M E, et al. (2000) Absence of alpha-syntrophin leads to     structurally aberrant neuromuscular synapses deficient in utrophin.     J Cell Biol 150(6):1385-1398. -   Betts, C. A., Hammond, S. M., Yin, H. F. & Wood, M. J. Optimizing     tissue-specific antisense oligonucleotide-Peptide conjugates.     Methods Mol Biol 867, 415-435 (2012). -   Bhagavati, S. Exon-skipping therapy for Duchenne muscular dystrophy.     Lancet 379, e10; author reply e10-11 (2012). -   Bostick, B., Ghosh, A., Yue, Y., Long, C. & Duan, D. Systemic AAV-9     transduction in mice is influenced by animal age but not by the     route of administration. Gene Ther 14, 1605-1609 (2007). -   Brenman J E, Chao D S, Xia H, Aldape K, Bredt D S (1995) Nitric     oxide synthase complexed with dystrophin and absent from skeletal     muscle sarcolemma in Duchenne muscular dystrophy. Cell     82(5):743-752. -   Brenman, J. E. et al. Interaction of nitric oxide synthase with the     postsynaptic density protein PSD-95 and alpha1-syntrophin mediated     by PDZ domains. Cell 84, 757-767 (1996). -   Chao D S, et al. (1996) Selective loss of sarcolemmal nitric oxide     synthase in Becker muscular dystrophy. J Exp Med 184(2):609-618. -   Choy, E. et al. Endomembrane trafficking of ras: the CAAX motif     targets proteins to the ER and Golgi. Cell 98, 69-80 (1999). -   Cirak, S. et al. Exon skipping and dystrophin restoration in     patients with Duchenne muscular dystrophy after systemic     phosphorodiamidate morpholino oligomer treatment: an open-label,     phase 2, doseescalation study. Lancet 378, 595-605 (2011). -   Djinovic-Carugo K, Gautel M, Ylänne J, Young P (2002) The spectrin     repeat: A structural platform for cytoskeletal protein assemblies.     FEBS Lett 513(1):119-123. -   England, S. B. et al. Very mild muscular dystrophy associated with     the deletion of 46% of dystrophin. Nature 343, 180-182 (1990). -   Foster, H. et al. Codon and mRNA sequence optimization of     microdystrophin transgenes improves expression and physiological     outcome in dystrophic mdx mice following AAV2/8 gene transfer. Mol     Ther 16, 1825-1832 (2008). -   Goemans, N. M. et al. Systemic administration of PRO051 in     Duchenne's muscular dystrophy. N Engl J Med 364, 1513-1522 (2011). -   Grady R M, et al. (1997) Skeletal and cardiac myopathies in mice     lacking utrophin and dystrophin: A model for Duchenne muscular     dystrophy. Cell 90(4):729-738. -   Gregorevic, P. et al. rAAV6-microdystrophin preserves muscle     function and extends lifespan in severely dystrophic mice. Nat Med     12, 787-789 (2006). -   Gregorevic, P. et al. Systemic delivery of genes to striated muscles     using adeno-associated viral vectors. Nat Med 10, 828-834 (2004). -   Hancock J F, Paterson H, Marshall C J (1990) A polybasic domain or     palmitoylation is required in addition to the CAAX motif to localize     p21 ras to the plasma membrane. Cell 63(1):133-139. -   Harper S Q, et al. (2002) Modular flexibility of dystrophin:     Implications for gene therapy of Duchenne muscular dystrophy. Nat     Med 8(3):253-261. -   Hillier B J, Christopherson K S, Prehoda K E, Bredt D S, Lim W     A (1999) Unexpected modes of PDZ domain scaffolding revealed by     structure of nNOS-syntrophin complex. Science 284(5415):812-815. -   Ho, A., Schwarze, S. R., Mermelstein, S. J., Waksman, G. &     Dowdy, S. F. Synthetic protein transduction domains: enhanced     transduction potential in vitro and in vivo. Cancer Res 61, 474-477     (2001). -   Hsieh, C. H. et al. MicroRNA profiling in ischemic injury of the     gracilis muscle in rats. BMC Musculoskelet Disord 11, 123 (2010). -   Inagaki, K. et al. Robust systemic transduction with AAV9 vectors in     mice: efficient global cardiac gene transfer superior to that of     AAV8. Mol Ther 14, 45-53 (2006). -   Ipsaro J J, Mondragón A (2010) Structural basis for spectrin     recognition by ankyrin. Blood 115(20):4093-4101. -   Ivanova, G. D. et al. Improved cell-penetrating peptide-PNA     conjugates for splicing redirection in HeLa cells and exon skipping     in mdx mouse muscle. Nucleic Acids Res 36, 6418-6428 (2008). -   Jearawiriyapaisarn, N. et al. Sustained dystrophin expression     induced by peptide-conjugated morpholino oligomers in the muscles of     mdx mice. Mol Ther 16, 1624-1629 (2008). -   Judge L M, Haraguchiln M, Chamberlain J S (2006) Dissecting the     signaling and mechanical functions of the dystrophin-glycoprotein     complex. J Cell Sci 119(Pt 8): 1537-1546. -   Kameya S, et al. (1999) alpha1-syntrophin gene disruption results in     the absence of neuronal-type nitric-oxide synthase at the sarcolemma     but does not induce muscle degeneration. J Biol Chem     274(4):2193-2200. -   Karnoub, A. E. & Weinberg, R. A. Ras oncogenes: split personalities.     Nat Rev Mol Cell Biol 9, 517-531 (2008). -   Kobayashi Y M, et al. (2008) Sarcolemma-localized nNOS is required     to maintain activity after mild exercise. Nature 456(7221):511-515. -   Kunkel L M (2005) 2004 William Allan Award address. Cloning of the     DMD gene. Am J Hum Genet 76(2):205-214. -   Kunkel L M (2005) 2004 William Allan Award address. Cloning of the     DMD gene. Am J Hum Genet 76(2):205-214. -   Lai Y, et al. (2005) Efficient in vivo gene expression by     trans-splicing adeno-associated viral vectors. Nat Biotechnol     23(11):1435-1439. -   Lai Y, et al. (2009) Dystrophins carrying spectrin-like repeats 16     and 17 anchor nNOS to the sarcolemma and enhance exercise     performance in a mouse model of muscular dystrophy. J Clin Invest     119(3):624-635. -   Le Rumeur E, Hubert J F, Winder S J (2012) A new twist to coiled     coil. FEBS Lett 586(17): 2717-2722. -   Le Rumeur E, Winder S J, Hubert J F (2010) Dystrophin: More than     just the sum of its parts. Biochim Biophys Acta 1804(9):1713-1722. -   Legrand B, Giudice E, Nicolas A, Delalande O, Le Rumeur E (2011)     Computational study of the human dystrophin repeats: interaction     properties and molecular -   Li D, et al. (2010) Sarcolemmal nNOS anchoring reveals a qualitative     difference between dystrophin and utrophin. J Cell Sci 123(Pt     12):2008-2013. -   Li D, Long C, Yue Y, Duan D (2009) Sub-physiological sarcoglycan     expression contributes to compensatory muscle protection in mdx     mice. Hum Mol Genet 18(7):1209-1220. -   Li D, Yue Y, Lai Y, Hakim C H, Duan D (2011a) Nitrosative stress     elicited by nNOSμ delocalization inhibits muscle force in     dystrophin-null mice. J Pathol 223(1):88-98. -   Li D, Shin J H, Duan D (2011 b) iNOS ablation does not improve     specific force of the extensor digitorum longus muscle in     dystrophin-deficient mdx4cv mice. PLoS ONE 6(6):e21618. -   Li, X., Eastman, E. M., Schwartz, R. J. & Draghia-Akli, R. Synthetic     muscle promoters: activities exceeding naturally occurring     regulatory sequences. Nat Biotechnol 17, 241-245 (1999). -   Morris G, Man N T, Sewry C A (2011) Monitoring duchenne muscular     dystrophy gene therapy with epitope-specific monoclonal antibodies.     Methods Mol Biol 709:39-61. -   Morris, M. C., Depollier, J., Mery, J., Heitz, F. & Divita, G. A     peptide carrier for the delivery of biologically active proteins     into mammalian cells. Nat Biotechnol 19, 1173-1176 (2001). -   Moulton, H. M. Cell-penetrating peptides enhance systemic delivery     of antisense morpholino oligomers. Methods Mol Biol 867, 407-414     (2012). -   Nakamura, A. & Takeda, S. Exon-skipping therapy for Duchenne     muscular dystrophy. Lancet 378, 546-547 (2011). -   Navarro-Lerida, I., Alvarez-Barrientos, A. & Rodriguez-Crespo, I.     N-terminal palmitoylation within the appropriate amino acid     environment conveys on NOS2 the ability to progress along the     intracellular sorting pathways. J Cell Sci 119, 1558-1569 (2006). -   Neri, M. et al. Dystrophin levels as low as 30% are sufficient to     avoid muscular dystrophy in the human. Neuromuscul Disord 17,     913-918 (2007). -   Nishida, C. R. & Ortiz de Montellano, P. R. Electron transfer and     catalytic activity of nitric oxide synthases. Chimeric constructs of     the neuronal, inducible, and endothelial isoforms. J Biol Chem 273,     5566-5571 (1998). -   Qiao C, et al. (2010) AAV6 capsid tyrosine to phenylalanine     mutations improve gene transfer to skeletal muscle. Hum Gene Ther     21(10):1343-1348. -   Roseguini, B. T. et al. Intermittent pneumatic leg compressions     acutely upregulate VEGF and MCP-1 expression in skeletal muscle. Am     J Physiol Heart Circ Physiol 298, H1991-2000 (2010). -   Rybakova I N, Patel J R, Davies K E, Yurchenco P D, Ervasti J     M (2002) Utrophin binds laterally along actin filaments and can     couple costameric actin with sarcolemma when overexpressed in     dystrophin-deficient muscle. Mol Biol Cell 13(5):1512-1521 -   Sander M, et al. (2000) Functional muscle ischemia in neuronal     nitric oxide synthase deficient skeletal muscle of children with     Duchenne muscular dystrophy. Proc Natl Acad Sci USA     97(25):13818-13823. -   Schwarze, S. R., Ho, A., Vocero-Akbani, A. & Dowdy, S. F. In vivo     protein transduction: delivery of a biologically active protein into     the mouse. Science 285, 1569-1572 (1999). -   Shin J H, Yue Y, Duan D (2012) Recombinant adeno-associated viral     vector production and purification. Methods Mol Biol 798:267-284. -   Sirsi, S. R. et al. Functionalized PEG-PEI copolymers complexed to     exon-skipping oligonucleotides improve dystrophin expression in mdx     mice. Hum Gene Ther 19, 795-806 (2008). -   Sonnemann, K. J. et al. Functional Substitution by TAT-Utrophin in     Dystrophin-Deficient Mice. PLoS Med 6, e1000083 (2009). -   Stabach P R, et al. (2009) The structure of the ankyrin-binding site     of beta-spectrin reveals how tandem spectrin-repeats generate unique     ligand-binding properties. Blood 113(22):5377-5384. -   Thomas G D, et al. (1998) Impaired metabolic modulation of     alpha-adrenergic vasoconstriction in dystrophin-deficient skeletal     muscle. Proc Natl Acad Sci USA 95(25): 15090-15095. -   Thomas, G. D., Shaul, P. W., Yuhanna, I. S., Froehner, S. C. &     Adams, M. E. Vasomodulation by skeletal muscle-derived nitric oxide     requires alphasyntrophin-mediated sarcolemmal localization of     neuronal Nitric oxide synthase. Circ Res 92, 554-560 (2003). -   Tochio H, Zhang Q, Mandal P, Li M, Zhang M (1999) Solution structure     of the extended neuronal nitric oxide synthase PDZ domain complexed     with an associated peptide. Nat Struct Biol 6(5):417-421. -   Torelli S, et al. (2004) Absence of neuronal nitric oxide synthase     (nNOS) as a pathological marker for the diagnosis of Becker muscular     dystrophy with rod domain deletions. Neuropathol Appl Neurobiol     30(5):540-545. -   van Deutekom, J. C. et al. Local dystrophin restoration with     antisense oligonucleotide PRO051. N Engl J Med 357, 2677-2686     (2007). -   Wang, B., Li, J. & Xiao, X. Adeno-associated virus vector carrying     human minidystrophin genes effectively ameliorates muscular     dystrophy in mdx mouse model. Proc Natl Acad Sci USA 97, 13714-13719     (2000). -   Wang, Q. et al. TAT-mediated protein transduction of Nogo     extracellular peptide 1-40 and its biological activity. Cell Mol     Neurobiol 29, 97-108 (2009). -   Wells K E, et al. (2003) Relocalization of neuronal nitric oxide     synthase (nNOS) as a marker for complete restoration of the     dystrophin associated protein complex in skeletal muscle.     Neuromuscul Disord 13(1):21-31. -   White, S. J. & den Dunnen, J. T. Copy number variation in the     genome; the human DMD gene as an example. Cytogenet Genome Res 115,     240-246 (2006). -   Wu, B. et al. Effective rescue of dystrophin improves cardiac     function in dystrophin-deficient mice by a modified morpholino     oligomer. Proc Natl Acad Sci USA 105, 14814-14819 (2008). -   Yin, H. et al. Cell-penetrating peptide-conjugated antisense     oligonucleotides restore systemic muscle and cardiac dystrophin     expression and function. Hum Mol Genet 17, 3909-3918 (2008). -   Yin, H. et al. A fusion peptide directs enhanced systemic dystrophin     exon skipping and functional restoration in dystrophin-deficient mdx     mice. Hum Mol Genet 18, 4405-4414 (2009). -   Yin, H. et al. Optimization of peptide nucleic acid antisense     oligonucleotides for local and systemic dystrophin splice correction     in the mdx mouse. Mol Ther 18, 819-827 (2010). -   Yokota, T. et al. Efficacy of systemic morpholino exon-skipping in     Duchenne dystrophy dogs. Ann Neurol 65, 667-676 (2009). -   Yue Y, Liu M, Duan D (2006) C-terminal-truncated microdystrophin     recruits dystrobrevin and syntrophin to the dystrophin-associated     glycoprotein complex and reduces muscular dystrophy in symptomatic     utrophin/dystrophin double-knockout mice. Mol Ther 14(1):79-87. -   Zhong L, et al. (2008) Next generation of adeno-associated virus 2     vectors: Point mutations in tyrosines lead to high-efficiency     transduction at lower doses. Proc Natl Acad Sci USA     105(22):7827-7832. 

What is claimed is:
 1. A therapeutic composition comprising: a microdystrophin peptide having an amino acid sequence which comprises dystrophin spectrin-like repeats 16 and 17 (R16/R17) (SEQ ID NO:7); and a delivery vehicle.
 2. The therapeutic composition of claim 1, wherein the delivery vehicle is a cell-penetrating peptide.
 3. The therapeutic composition of claim 1, wherein the cell penetrating peptide is conjugated to the amino acid sequence comprising R16/R17 at the cell penetrating peptide protein transduction domain.
 4. The therapeutic composition of claim 2, wherein the cell-penetrating peptide is TAT (YGRKKRRQRRR; SEQ ID NO:48).
 5. The therapeutic composition of claim 1, wherein the delivery vehicle is a recombinant adeno-associated virus (AAV) vector, and wherein the AAV vector expresses the amino acid sequence comprising R16/R17.
 6. The therapeutic composition of claim 1, wherein the therapeutic composition is used to treat Duchenne Muscular Dystrophy (DMD), Becker Muscular Dystrophy (BMD) or X-linked dilated cardiomyopathy (XLDC).
 7. A therapeutic composition comprising: an amino acid sequence motif which comprises RFHYDIKIFN (SEQ ID NO:46); and a delivery vehicle.
 8. The therapeutic composition of claim 7, wherein the therapeutic composition further comprises: at least one α helix of dystrophin spectrin-like repeat 16 (R16); and at least one α helix of dystrophin spectrin-like repeat 17 (R17).
 9. The therapeutic composition of claim 8, wherein the therapeutic composition comprises: an α2 helix and an α3 helix of R16; and an α2 helix and an α3 helix of R17.
 10. The therapeutic composition of claim 7, wherein the delivery vehicle is a cell-penetrating peptide.
 11. The therapeutic composition of claim 7, wherein the cell penetrating peptide is conjugated to the amino acid sequence RFHYDIKIFN (SEQ ID NO:46) at the cell penetrating peptide protein transduction domain.
 12. The therapeutic composition of claim 10, wherein the cell-penetrating peptide is TAT (YGRKKRRQRRR; SEQ ID NO:48).
 13. The therapeutic composition of claim 7, wherein the delivery vehicle is an recombinant adeno-associated virus (AAV) vector, and wherein the AAV vector expresses the amino acid sequence comprising R16/R17.
 14. The therapeutic composition of claim 7, wherein the therapeutic composition is used to treat Duchenne Muscular Dystrophy (DMD) or Becker Muscular Dystrophy (BMD), or X-linked dilated cardiomyopathy (XLDC).
 15. A method of treating DMD, BMD or XLDC comprising administering a therapeutic amount of a therapeutic composition to a subject having DMD or BMD, wherein the therapeutic composition comprises an amino acid sequence motif RFHYDIKIFN (SEQ ID NO:46); and a delivery vehicle.
 16. The method of claim 15, wherein the therapeutic composition further comprises: at least one α helix of dystrophin spectrin-like repeat 16 (R16); and at least one α helix of dystrophin spectrin-like repeat 17 (R17).
 17. The method of claim 16, wherein the therapeutic composition comprises: an α2 helix and an α3 helix of R16; and an α2 helix and an α3 helix of R17.
 18. The method of claim 15, wherein the delivery vehicle is a cell-penetrating peptide.
 19. The method of claim 15, wherein the cell penetrating peptide is conjugated to the amino acid sequence comprising R16/R17 at the cell penetrating peptide protein transduction domain.
 20. The method of claim 18, wherein the cell-penetrating peptide is TAT (YGRKKRRQRRR; SEQ ID NO:48).
 21. The method of claim 15, wherein the delivery vehicle is an recombinant adeno-associated virus (AAV) vector, and wherein the AAV vector expresses the amino acid sequence comprising R16/R17. 